Source file src/net/http/server.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // HTTP server. See RFC 7230 through 7235.
     6  
     7  package http
     8  
     9  import (
    10  	"bufio"
    11  	"bytes"
    12  	"context"
    13  	"crypto/tls"
    14  	"errors"
    15  	"fmt"
    16  	"internal/godebug"
    17  	"io"
    18  	"log"
    19  	"maps"
    20  	"math/rand"
    21  	"net"
    22  	"net/textproto"
    23  	"net/url"
    24  	urlpkg "net/url"
    25  	"path"
    26  	"runtime"
    27  	"slices"
    28  	"strconv"
    29  	"strings"
    30  	"sync"
    31  	"sync/atomic"
    32  	"time"
    33  	_ "unsafe" // for linkname
    34  
    35  	"golang.org/x/net/http/httpguts"
    36  )
    37  
    38  // Errors used by the HTTP server.
    39  var (
    40  	// ErrBodyNotAllowed is returned by ResponseWriter.Write calls
    41  	// when the HTTP method or response code does not permit a
    42  	// body.
    43  	ErrBodyNotAllowed = errors.New("http: request method or response status code does not allow body")
    44  
    45  	// ErrHijacked is returned by ResponseWriter.Write calls when
    46  	// the underlying connection has been hijacked using the
    47  	// Hijacker interface. A zero-byte write on a hijacked
    48  	// connection will return ErrHijacked without any other side
    49  	// effects.
    50  	ErrHijacked = errors.New("http: connection has been hijacked")
    51  
    52  	// ErrContentLength is returned by ResponseWriter.Write calls
    53  	// when a Handler set a Content-Length response header with a
    54  	// declared size and then attempted to write more bytes than
    55  	// declared.
    56  	ErrContentLength = errors.New("http: wrote more than the declared Content-Length")
    57  
    58  	// Deprecated: ErrWriteAfterFlush is no longer returned by
    59  	// anything in the net/http package. Callers should not
    60  	// compare errors against this variable.
    61  	ErrWriteAfterFlush = errors.New("unused")
    62  )
    63  
    64  // A Handler responds to an HTTP request.
    65  //
    66  // [Handler.ServeHTTP] should write reply headers and data to the [ResponseWriter]
    67  // and then return. Returning signals that the request is finished; it
    68  // is not valid to use the [ResponseWriter] or read from the
    69  // [Request.Body] after or concurrently with the completion of the
    70  // ServeHTTP call.
    71  //
    72  // Depending on the HTTP client software, HTTP protocol version, and
    73  // any intermediaries between the client and the Go server, it may not
    74  // be possible to read from the [Request.Body] after writing to the
    75  // [ResponseWriter]. Cautious handlers should read the [Request.Body]
    76  // first, and then reply.
    77  //
    78  // Except for reading the body, handlers should not modify the
    79  // provided Request.
    80  //
    81  // If ServeHTTP panics, the server (the caller of ServeHTTP) assumes
    82  // that the effect of the panic was isolated to the active request.
    83  // It recovers the panic, logs a stack trace to the server error log,
    84  // and either closes the network connection or sends an HTTP/2
    85  // RST_STREAM, depending on the HTTP protocol. To abort a handler so
    86  // the client sees an interrupted response but the server doesn't log
    87  // an error, panic with the value [ErrAbortHandler].
    88  type Handler interface {
    89  	ServeHTTP(ResponseWriter, *Request)
    90  }
    91  
    92  // A ResponseWriter interface is used by an HTTP handler to
    93  // construct an HTTP response.
    94  //
    95  // A ResponseWriter may not be used after [Handler.ServeHTTP] has returned.
    96  type ResponseWriter interface {
    97  	// Header returns the header map that will be sent by
    98  	// [ResponseWriter.WriteHeader]. The [Header] map also is the mechanism with which
    99  	// [Handler] implementations can set HTTP trailers.
   100  	//
   101  	// Changing the header map after a call to [ResponseWriter.WriteHeader] (or
   102  	// [ResponseWriter.Write]) has no effect unless the HTTP status code was of the
   103  	// 1xx class or the modified headers are trailers.
   104  	//
   105  	// There are two ways to set Trailers. The preferred way is to
   106  	// predeclare in the headers which trailers you will later
   107  	// send by setting the "Trailer" header to the names of the
   108  	// trailer keys which will come later. In this case, those
   109  	// keys of the Header map are treated as if they were
   110  	// trailers. See the example. The second way, for trailer
   111  	// keys not known to the [Handler] until after the first [ResponseWriter.Write],
   112  	// is to prefix the [Header] map keys with the [TrailerPrefix]
   113  	// constant value.
   114  	//
   115  	// To suppress automatic response headers (such as "Date"), set
   116  	// their value to nil.
   117  	Header() Header
   118  
   119  	// Write writes the data to the connection as part of an HTTP reply.
   120  	//
   121  	// If [ResponseWriter.WriteHeader] has not yet been called, Write calls
   122  	// WriteHeader(http.StatusOK) before writing the data. If the Header
   123  	// does not contain a Content-Type line, Write adds a Content-Type set
   124  	// to the result of passing the initial 512 bytes of written data to
   125  	// [DetectContentType]. Additionally, if the total size of all written
   126  	// data is under a few KB and there are no Flush calls, the
   127  	// Content-Length header is added automatically.
   128  	//
   129  	// Depending on the HTTP protocol version and the client, calling
   130  	// Write or WriteHeader may prevent future reads on the
   131  	// Request.Body. For HTTP/1.x requests, handlers should read any
   132  	// needed request body data before writing the response. Once the
   133  	// headers have been flushed (due to either an explicit Flusher.Flush
   134  	// call or writing enough data to trigger a flush), the request body
   135  	// may be unavailable. For HTTP/2 requests, the Go HTTP server permits
   136  	// handlers to continue to read the request body while concurrently
   137  	// writing the response. However, such behavior may not be supported
   138  	// by all HTTP/2 clients. Handlers should read before writing if
   139  	// possible to maximize compatibility.
   140  	Write([]byte) (int, error)
   141  
   142  	// WriteHeader sends an HTTP response header with the provided
   143  	// status code.
   144  	//
   145  	// If WriteHeader is not called explicitly, the first call to Write
   146  	// will trigger an implicit WriteHeader(http.StatusOK).
   147  	// Thus explicit calls to WriteHeader are mainly used to
   148  	// send error codes or 1xx informational responses.
   149  	//
   150  	// The provided code must be a valid HTTP 1xx-5xx status code.
   151  	// Any number of 1xx headers may be written, followed by at most
   152  	// one 2xx-5xx header. 1xx headers are sent immediately, but 2xx-5xx
   153  	// headers may be buffered. Use the Flusher interface to send
   154  	// buffered data. The header map is cleared when 2xx-5xx headers are
   155  	// sent, but not with 1xx headers.
   156  	//
   157  	// The server will automatically send a 100 (Continue) header
   158  	// on the first read from the request body if the request has
   159  	// an "Expect: 100-continue" header.
   160  	WriteHeader(statusCode int)
   161  }
   162  
   163  // The Flusher interface is implemented by ResponseWriters that allow
   164  // an HTTP handler to flush buffered data to the client.
   165  //
   166  // The default HTTP/1.x and HTTP/2 [ResponseWriter] implementations
   167  // support [Flusher], but ResponseWriter wrappers may not. Handlers
   168  // should always test for this ability at runtime.
   169  //
   170  // Note that even for ResponseWriters that support Flush,
   171  // if the client is connected through an HTTP proxy,
   172  // the buffered data may not reach the client until the response
   173  // completes.
   174  type Flusher interface {
   175  	// Flush sends any buffered data to the client.
   176  	Flush()
   177  }
   178  
   179  // The Hijacker interface is implemented by ResponseWriters that allow
   180  // an HTTP handler to take over the connection.
   181  //
   182  // The default [ResponseWriter] for HTTP/1.x connections supports
   183  // Hijacker, but HTTP/2 connections intentionally do not.
   184  // ResponseWriter wrappers may also not support Hijacker. Handlers
   185  // should always test for this ability at runtime.
   186  type Hijacker interface {
   187  	// Hijack lets the caller take over the connection.
   188  	// After a call to Hijack the HTTP server library
   189  	// will not do anything else with the connection.
   190  	//
   191  	// It becomes the caller's responsibility to manage
   192  	// and close the connection.
   193  	//
   194  	// The returned net.Conn may have read or write deadlines
   195  	// already set, depending on the configuration of the
   196  	// Server. It is the caller's responsibility to set
   197  	// or clear those deadlines as needed.
   198  	//
   199  	// The returned bufio.Reader may contain unprocessed buffered
   200  	// data from the client.
   201  	//
   202  	// After a call to Hijack, the original Request.Body must not
   203  	// be used. The original Request's Context remains valid and
   204  	// is not canceled until the Request's ServeHTTP method
   205  	// returns.
   206  	Hijack() (net.Conn, *bufio.ReadWriter, error)
   207  }
   208  
   209  // The CloseNotifier interface is implemented by ResponseWriters which
   210  // allow detecting when the underlying connection has gone away.
   211  //
   212  // This mechanism can be used to cancel long operations on the server
   213  // if the client has disconnected before the response is ready.
   214  //
   215  // Deprecated: the CloseNotifier interface predates Go's context package.
   216  // New code should use [Request.Context] instead.
   217  type CloseNotifier interface {
   218  	// CloseNotify returns a channel that receives at most a
   219  	// single value (true) when the client connection has gone
   220  	// away.
   221  	//
   222  	// CloseNotify may wait to notify until Request.Body has been
   223  	// fully read.
   224  	//
   225  	// After the Handler has returned, there is no guarantee
   226  	// that the channel receives a value.
   227  	//
   228  	// If the protocol is HTTP/1.1 and CloseNotify is called while
   229  	// processing an idempotent request (such as GET) while
   230  	// HTTP/1.1 pipelining is in use, the arrival of a subsequent
   231  	// pipelined request may cause a value to be sent on the
   232  	// returned channel. In practice HTTP/1.1 pipelining is not
   233  	// enabled in browsers and not seen often in the wild. If this
   234  	// is a problem, use HTTP/2 or only use CloseNotify on methods
   235  	// such as POST.
   236  	CloseNotify() <-chan bool
   237  }
   238  
   239  var (
   240  	// ServerContextKey is a context key. It can be used in HTTP
   241  	// handlers with Context.Value to access the server that
   242  	// started the handler. The associated value will be of
   243  	// type *Server.
   244  	ServerContextKey = &contextKey{"http-server"}
   245  
   246  	// LocalAddrContextKey is a context key. It can be used in
   247  	// HTTP handlers with Context.Value to access the local
   248  	// address the connection arrived on.
   249  	// The associated value will be of type net.Addr.
   250  	LocalAddrContextKey = &contextKey{"local-addr"}
   251  )
   252  
   253  // A conn represents the server side of an HTTP connection.
   254  type conn struct {
   255  	// server is the server on which the connection arrived.
   256  	// Immutable; never nil.
   257  	server *Server
   258  
   259  	// cancelCtx cancels the connection-level context.
   260  	cancelCtx context.CancelFunc
   261  
   262  	// rwc is the underlying network connection.
   263  	// This is never wrapped by other types and is the value given out
   264  	// to [Hijacker] callers. It is usually of type *net.TCPConn or
   265  	// *tls.Conn.
   266  	rwc net.Conn
   267  
   268  	// remoteAddr is rwc.RemoteAddr().String(). It is not populated synchronously
   269  	// inside the Listener's Accept goroutine, as some implementations block.
   270  	// It is populated immediately inside the (*conn).serve goroutine.
   271  	// This is the value of a Handler's (*Request).RemoteAddr.
   272  	remoteAddr string
   273  
   274  	// tlsState is the TLS connection state when using TLS.
   275  	// nil means not TLS.
   276  	tlsState *tls.ConnectionState
   277  
   278  	// werr is set to the first write error to rwc.
   279  	// It is set via checkConnErrorWriter{w}, where bufw writes.
   280  	werr error
   281  
   282  	// r is bufr's read source. It's a wrapper around rwc that provides
   283  	// io.LimitedReader-style limiting (while reading request headers)
   284  	// and functionality to support CloseNotifier. See *connReader docs.
   285  	r *connReader
   286  
   287  	// bufr reads from r.
   288  	bufr *bufio.Reader
   289  
   290  	// bufw writes to checkConnErrorWriter{c}, which populates werr on error.
   291  	bufw *bufio.Writer
   292  
   293  	// lastMethod is the method of the most recent request
   294  	// on this connection, if any.
   295  	lastMethod string
   296  
   297  	curReq atomic.Pointer[response] // (which has a Request in it)
   298  
   299  	curState atomic.Uint64 // packed (unixtime<<8|uint8(ConnState))
   300  
   301  	// mu guards hijackedv
   302  	mu sync.Mutex
   303  
   304  	// hijackedv is whether this connection has been hijacked
   305  	// by a Handler with the Hijacker interface.
   306  	// It is guarded by mu.
   307  	hijackedv bool
   308  }
   309  
   310  func (c *conn) hijacked() bool {
   311  	c.mu.Lock()
   312  	defer c.mu.Unlock()
   313  	return c.hijackedv
   314  }
   315  
   316  // c.mu must be held.
   317  func (c *conn) hijackLocked() (rwc net.Conn, buf *bufio.ReadWriter, err error) {
   318  	if c.hijackedv {
   319  		return nil, nil, ErrHijacked
   320  	}
   321  	c.r.abortPendingRead()
   322  
   323  	c.hijackedv = true
   324  	rwc = c.rwc
   325  	rwc.SetDeadline(time.Time{})
   326  
   327  	buf = bufio.NewReadWriter(c.bufr, bufio.NewWriter(rwc))
   328  	if c.r.hasByte {
   329  		if _, err := c.bufr.Peek(c.bufr.Buffered() + 1); err != nil {
   330  			return nil, nil, fmt.Errorf("unexpected Peek failure reading buffered byte: %v", err)
   331  		}
   332  	}
   333  	c.setState(rwc, StateHijacked, runHooks)
   334  	return
   335  }
   336  
   337  // This should be >= 512 bytes for DetectContentType,
   338  // but otherwise it's somewhat arbitrary.
   339  const bufferBeforeChunkingSize = 2048
   340  
   341  // chunkWriter writes to a response's conn buffer, and is the writer
   342  // wrapped by the response.w buffered writer.
   343  //
   344  // chunkWriter also is responsible for finalizing the Header, including
   345  // conditionally setting the Content-Type and setting a Content-Length
   346  // in cases where the handler's final output is smaller than the buffer
   347  // size. It also conditionally adds chunk headers, when in chunking mode.
   348  //
   349  // See the comment above (*response).Write for the entire write flow.
   350  type chunkWriter struct {
   351  	res *response
   352  
   353  	// header is either nil or a deep clone of res.handlerHeader
   354  	// at the time of res.writeHeader, if res.writeHeader is
   355  	// called and extra buffering is being done to calculate
   356  	// Content-Type and/or Content-Length.
   357  	header Header
   358  
   359  	// wroteHeader tells whether the header's been written to "the
   360  	// wire" (or rather: w.conn.buf). this is unlike
   361  	// (*response).wroteHeader, which tells only whether it was
   362  	// logically written.
   363  	wroteHeader bool
   364  
   365  	// set by the writeHeader method:
   366  	chunking bool // using chunked transfer encoding for reply body
   367  }
   368  
   369  var (
   370  	crlf       = []byte("\r\n")
   371  	colonSpace = []byte(": ")
   372  )
   373  
   374  func (cw *chunkWriter) Write(p []byte) (n int, err error) {
   375  	if !cw.wroteHeader {
   376  		cw.writeHeader(p)
   377  	}
   378  	if cw.res.req.Method == "HEAD" {
   379  		// Eat writes.
   380  		return len(p), nil
   381  	}
   382  	if cw.chunking {
   383  		_, err = fmt.Fprintf(cw.res.conn.bufw, "%x\r\n", len(p))
   384  		if err != nil {
   385  			cw.res.conn.rwc.Close()
   386  			return
   387  		}
   388  	}
   389  	n, err = cw.res.conn.bufw.Write(p)
   390  	if cw.chunking && err == nil {
   391  		_, err = cw.res.conn.bufw.Write(crlf)
   392  	}
   393  	if err != nil {
   394  		cw.res.conn.rwc.Close()
   395  	}
   396  	return
   397  }
   398  
   399  func (cw *chunkWriter) flush() error {
   400  	if !cw.wroteHeader {
   401  		cw.writeHeader(nil)
   402  	}
   403  	return cw.res.conn.bufw.Flush()
   404  }
   405  
   406  func (cw *chunkWriter) close() {
   407  	if !cw.wroteHeader {
   408  		cw.writeHeader(nil)
   409  	}
   410  	if cw.chunking {
   411  		bw := cw.res.conn.bufw // conn's bufio writer
   412  		// zero chunk to mark EOF
   413  		bw.WriteString("0\r\n")
   414  		if trailers := cw.res.finalTrailers(); trailers != nil {
   415  			trailers.Write(bw) // the writer handles noting errors
   416  		}
   417  		// final blank line after the trailers (whether
   418  		// present or not)
   419  		bw.WriteString("\r\n")
   420  	}
   421  }
   422  
   423  // A response represents the server side of an HTTP response.
   424  type response struct {
   425  	conn             *conn
   426  	req              *Request // request for this response
   427  	reqBody          io.ReadCloser
   428  	cancelCtx        context.CancelFunc // when ServeHTTP exits
   429  	wroteHeader      bool               // a non-1xx header has been (logically) written
   430  	wants10KeepAlive bool               // HTTP/1.0 w/ Connection "keep-alive"
   431  	wantsClose       bool               // HTTP request has Connection "close"
   432  
   433  	// canWriteContinue is an atomic boolean that says whether or
   434  	// not a 100 Continue header can be written to the
   435  	// connection.
   436  	// writeContinueMu must be held while writing the header.
   437  	// These two fields together synchronize the body reader (the
   438  	// expectContinueReader, which wants to write 100 Continue)
   439  	// against the main writer.
   440  	writeContinueMu  sync.Mutex
   441  	canWriteContinue atomic.Bool
   442  
   443  	w  *bufio.Writer // buffers output in chunks to chunkWriter
   444  	cw chunkWriter
   445  
   446  	// handlerHeader is the Header that Handlers get access to,
   447  	// which may be retained and mutated even after WriteHeader.
   448  	// handlerHeader is copied into cw.header at WriteHeader
   449  	// time, and privately mutated thereafter.
   450  	handlerHeader Header
   451  	calledHeader  bool // handler accessed handlerHeader via Header
   452  
   453  	written       int64 // number of bytes written in body
   454  	contentLength int64 // explicitly-declared Content-Length; or -1
   455  	status        int   // status code passed to WriteHeader
   456  
   457  	// close connection after this reply.  set on request and
   458  	// updated after response from handler if there's a
   459  	// "Connection: keep-alive" response header and a
   460  	// Content-Length.
   461  	closeAfterReply bool
   462  
   463  	// When fullDuplex is false (the default), we consume any remaining
   464  	// request body before starting to write a response.
   465  	fullDuplex bool
   466  
   467  	// requestBodyLimitHit is set by requestTooLarge when
   468  	// maxBytesReader hits its max size. It is checked in
   469  	// WriteHeader, to make sure we don't consume the
   470  	// remaining request body to try to advance to the next HTTP
   471  	// request. Instead, when this is set, we stop reading
   472  	// subsequent requests on this connection and stop reading
   473  	// input from it.
   474  	requestBodyLimitHit bool
   475  
   476  	// trailers are the headers to be sent after the handler
   477  	// finishes writing the body. This field is initialized from
   478  	// the Trailer response header when the response header is
   479  	// written.
   480  	trailers []string
   481  
   482  	handlerDone atomic.Bool // set true when the handler exits
   483  
   484  	// Buffers for Date, Content-Length, and status code
   485  	dateBuf   [len(TimeFormat)]byte
   486  	clenBuf   [10]byte
   487  	statusBuf [3]byte
   488  
   489  	// lazyCloseNotifyMu protects closeNotifyCh and closeNotifyTriggered.
   490  	lazyCloseNotifyMu sync.Mutex
   491  	// closeNotifyCh is the channel returned by CloseNotify.
   492  	closeNotifyCh chan bool
   493  	// closeNotifyTriggered tracks prior closeNotify calls.
   494  	closeNotifyTriggered bool
   495  }
   496  
   497  func (c *response) SetReadDeadline(deadline time.Time) error {
   498  	return c.conn.rwc.SetReadDeadline(deadline)
   499  }
   500  
   501  func (c *response) SetWriteDeadline(deadline time.Time) error {
   502  	return c.conn.rwc.SetWriteDeadline(deadline)
   503  }
   504  
   505  func (c *response) EnableFullDuplex() error {
   506  	c.fullDuplex = true
   507  	return nil
   508  }
   509  
   510  // TrailerPrefix is a magic prefix for [ResponseWriter.Header] map keys
   511  // that, if present, signals that the map entry is actually for
   512  // the response trailers, and not the response headers. The prefix
   513  // is stripped after the ServeHTTP call finishes and the values are
   514  // sent in the trailers.
   515  //
   516  // This mechanism is intended only for trailers that are not known
   517  // prior to the headers being written. If the set of trailers is fixed
   518  // or known before the header is written, the normal Go trailers mechanism
   519  // is preferred:
   520  //
   521  //	https://pkg.go.dev/net/http#ResponseWriter
   522  //	https://pkg.go.dev/net/http#example-ResponseWriter-Trailers
   523  const TrailerPrefix = "Trailer:"
   524  
   525  // finalTrailers is called after the Handler exits and returns a non-nil
   526  // value if the Handler set any trailers.
   527  func (w *response) finalTrailers() Header {
   528  	var t Header
   529  	for k, vv := range w.handlerHeader {
   530  		if kk, found := strings.CutPrefix(k, TrailerPrefix); found {
   531  			if t == nil {
   532  				t = make(Header)
   533  			}
   534  			t[kk] = vv
   535  		}
   536  	}
   537  	for _, k := range w.trailers {
   538  		if t == nil {
   539  			t = make(Header)
   540  		}
   541  		for _, v := range w.handlerHeader[k] {
   542  			t.Add(k, v)
   543  		}
   544  	}
   545  	return t
   546  }
   547  
   548  // declareTrailer is called for each Trailer header when the
   549  // response header is written. It notes that a header will need to be
   550  // written in the trailers at the end of the response.
   551  func (w *response) declareTrailer(k string) {
   552  	k = CanonicalHeaderKey(k)
   553  	if !httpguts.ValidTrailerHeader(k) {
   554  		// Forbidden by RFC 7230, section 4.1.2
   555  		return
   556  	}
   557  	w.trailers = append(w.trailers, k)
   558  }
   559  
   560  // requestTooLarge is called by maxBytesReader when too much input has
   561  // been read from the client.
   562  func (w *response) requestTooLarge() {
   563  	w.closeAfterReply = true
   564  	w.requestBodyLimitHit = true
   565  	if !w.wroteHeader {
   566  		w.Header().Set("Connection", "close")
   567  	}
   568  }
   569  
   570  // disableWriteContinue stops Request.Body.Read from sending an automatic 100-Continue.
   571  // If a 100-Continue is being written, it waits for it to complete before continuing.
   572  func (w *response) disableWriteContinue() {
   573  	w.writeContinueMu.Lock()
   574  	w.canWriteContinue.Store(false)
   575  	w.writeContinueMu.Unlock()
   576  }
   577  
   578  // writerOnly hides an io.Writer value's optional ReadFrom method
   579  // from io.Copy.
   580  type writerOnly struct {
   581  	io.Writer
   582  }
   583  
   584  // ReadFrom is here to optimize copying from an [*os.File] regular file
   585  // to a [*net.TCPConn] with sendfile, or from a supported src type such
   586  // as a *net.TCPConn on Linux with splice.
   587  func (w *response) ReadFrom(src io.Reader) (n int64, err error) {
   588  	buf := getCopyBuf()
   589  	defer putCopyBuf(buf)
   590  
   591  	// Our underlying w.conn.rwc is usually a *TCPConn (with its
   592  	// own ReadFrom method). If not, just fall back to the normal
   593  	// copy method.
   594  	rf, ok := w.conn.rwc.(io.ReaderFrom)
   595  	if !ok {
   596  		return io.CopyBuffer(writerOnly{w}, src, buf)
   597  	}
   598  
   599  	// Copy the first sniffLen bytes before switching to ReadFrom.
   600  	// This ensures we don't start writing the response before the
   601  	// source is available (see golang.org/issue/5660) and provides
   602  	// enough bytes to perform Content-Type sniffing when required.
   603  	if !w.cw.wroteHeader {
   604  		n0, err := io.CopyBuffer(writerOnly{w}, io.LimitReader(src, sniffLen), buf)
   605  		n += n0
   606  		if err != nil || n0 < sniffLen {
   607  			return n, err
   608  		}
   609  	}
   610  
   611  	w.w.Flush()  // get rid of any previous writes
   612  	w.cw.flush() // make sure Header is written; flush data to rwc
   613  
   614  	// Now that cw has been flushed, its chunking field is guaranteed initialized.
   615  	if !w.cw.chunking && w.bodyAllowed() && w.req.Method != "HEAD" {
   616  		n0, err := rf.ReadFrom(src)
   617  		n += n0
   618  		w.written += n0
   619  		return n, err
   620  	}
   621  
   622  	n0, err := io.CopyBuffer(writerOnly{w}, src, buf)
   623  	n += n0
   624  	return n, err
   625  }
   626  
   627  // debugServerConnections controls whether all server connections are wrapped
   628  // with a verbose logging wrapper.
   629  const debugServerConnections = false
   630  
   631  // Create new connection from rwc.
   632  func (s *Server) newConn(rwc net.Conn) *conn {
   633  	c := &conn{
   634  		server: s,
   635  		rwc:    rwc,
   636  	}
   637  	if debugServerConnections {
   638  		c.rwc = newLoggingConn("server", c.rwc)
   639  	}
   640  	return c
   641  }
   642  
   643  type readResult struct {
   644  	_   incomparable
   645  	n   int
   646  	err error
   647  	b   byte // byte read, if n == 1
   648  }
   649  
   650  // connReader is the io.Reader wrapper used by *conn. It combines a
   651  // selectively-activated io.LimitedReader (to bound request header
   652  // read sizes) with support for selectively keeping an io.Reader.Read
   653  // call blocked in a background goroutine to wait for activity and
   654  // trigger a CloseNotifier channel.
   655  type connReader struct {
   656  	conn *conn
   657  
   658  	mu      sync.Mutex // guards following
   659  	hasByte bool
   660  	byteBuf [1]byte
   661  	cond    *sync.Cond
   662  	inRead  bool
   663  	aborted bool  // set true before conn.rwc deadline is set to past
   664  	remain  int64 // bytes remaining
   665  }
   666  
   667  func (cr *connReader) lock() {
   668  	cr.mu.Lock()
   669  	if cr.cond == nil {
   670  		cr.cond = sync.NewCond(&cr.mu)
   671  	}
   672  }
   673  
   674  func (cr *connReader) unlock() { cr.mu.Unlock() }
   675  
   676  func (cr *connReader) startBackgroundRead() {
   677  	cr.lock()
   678  	defer cr.unlock()
   679  	if cr.inRead {
   680  		panic("invalid concurrent Body.Read call")
   681  	}
   682  	if cr.hasByte {
   683  		return
   684  	}
   685  	cr.inRead = true
   686  	cr.conn.rwc.SetReadDeadline(time.Time{})
   687  	go cr.backgroundRead()
   688  }
   689  
   690  func (cr *connReader) backgroundRead() {
   691  	n, err := cr.conn.rwc.Read(cr.byteBuf[:])
   692  	cr.lock()
   693  	if n == 1 {
   694  		cr.hasByte = true
   695  		// We were past the end of the previous request's body already
   696  		// (since we wouldn't be in a background read otherwise), so
   697  		// this is a pipelined HTTP request. Prior to Go 1.11 we used to
   698  		// send on the CloseNotify channel and cancel the context here,
   699  		// but the behavior was documented as only "may", and we only
   700  		// did that because that's how CloseNotify accidentally behaved
   701  		// in very early Go releases prior to context support. Once we
   702  		// added context support, people used a Handler's
   703  		// Request.Context() and passed it along. Having that context
   704  		// cancel on pipelined HTTP requests caused problems.
   705  		// Fortunately, almost nothing uses HTTP/1.x pipelining.
   706  		// Unfortunately, apt-get does, or sometimes does.
   707  		// New Go 1.11 behavior: don't fire CloseNotify or cancel
   708  		// contexts on pipelined requests. Shouldn't affect people, but
   709  		// fixes cases like Issue 23921. This does mean that a client
   710  		// closing their TCP connection after sending a pipelined
   711  		// request won't cancel the context, but we'll catch that on any
   712  		// write failure (in checkConnErrorWriter.Write).
   713  		// If the server never writes, yes, there are still contrived
   714  		// server & client behaviors where this fails to ever cancel the
   715  		// context, but that's kinda why HTTP/1.x pipelining died
   716  		// anyway.
   717  	}
   718  	if ne, ok := err.(net.Error); ok && cr.aborted && ne.Timeout() {
   719  		// Ignore this error. It's the expected error from
   720  		// another goroutine calling abortPendingRead.
   721  	} else if err != nil {
   722  		cr.handleReadError(err)
   723  	}
   724  	cr.aborted = false
   725  	cr.inRead = false
   726  	cr.unlock()
   727  	cr.cond.Broadcast()
   728  }
   729  
   730  func (cr *connReader) abortPendingRead() {
   731  	cr.lock()
   732  	defer cr.unlock()
   733  	if !cr.inRead {
   734  		return
   735  	}
   736  	cr.aborted = true
   737  	cr.conn.rwc.SetReadDeadline(aLongTimeAgo)
   738  	for cr.inRead {
   739  		cr.cond.Wait()
   740  	}
   741  	cr.conn.rwc.SetReadDeadline(time.Time{})
   742  }
   743  
   744  func (cr *connReader) setReadLimit(remain int64) { cr.remain = remain }
   745  func (cr *connReader) setInfiniteReadLimit()     { cr.remain = maxInt64 }
   746  func (cr *connReader) hitReadLimit() bool        { return cr.remain <= 0 }
   747  
   748  // handleReadError is called whenever a Read from the client returns a
   749  // non-nil error.
   750  //
   751  // The provided non-nil err is almost always io.EOF or a "use of
   752  // closed network connection". In any case, the error is not
   753  // particularly interesting, except perhaps for debugging during
   754  // development. Any error means the connection is dead and we should
   755  // down its context.
   756  //
   757  // It may be called from multiple goroutines.
   758  func (cr *connReader) handleReadError(_ error) {
   759  	cr.conn.cancelCtx()
   760  	cr.closeNotify()
   761  }
   762  
   763  // may be called from multiple goroutines.
   764  func (cr *connReader) closeNotify() {
   765  	if res := cr.conn.curReq.Load(); res != nil {
   766  		res.closeNotify()
   767  	}
   768  }
   769  
   770  func (cr *connReader) Read(p []byte) (n int, err error) {
   771  	cr.lock()
   772  	if cr.inRead {
   773  		cr.unlock()
   774  		if cr.conn.hijacked() {
   775  			panic("invalid Body.Read call. After hijacked, the original Request must not be used")
   776  		}
   777  		panic("invalid concurrent Body.Read call")
   778  	}
   779  	if cr.hitReadLimit() {
   780  		cr.unlock()
   781  		return 0, io.EOF
   782  	}
   783  	if len(p) == 0 {
   784  		cr.unlock()
   785  		return 0, nil
   786  	}
   787  	if int64(len(p)) > cr.remain {
   788  		p = p[:cr.remain]
   789  	}
   790  	if cr.hasByte {
   791  		p[0] = cr.byteBuf[0]
   792  		cr.hasByte = false
   793  		cr.unlock()
   794  		return 1, nil
   795  	}
   796  	cr.inRead = true
   797  	cr.unlock()
   798  	n, err = cr.conn.rwc.Read(p)
   799  
   800  	cr.lock()
   801  	cr.inRead = false
   802  	if err != nil {
   803  		cr.handleReadError(err)
   804  	}
   805  	cr.remain -= int64(n)
   806  	cr.unlock()
   807  
   808  	cr.cond.Broadcast()
   809  	return n, err
   810  }
   811  
   812  var (
   813  	bufioReaderPool   sync.Pool
   814  	bufioWriter2kPool sync.Pool
   815  	bufioWriter4kPool sync.Pool
   816  )
   817  
   818  const copyBufPoolSize = 32 * 1024
   819  
   820  var copyBufPool = sync.Pool{New: func() any { return new([copyBufPoolSize]byte) }}
   821  
   822  func getCopyBuf() []byte {
   823  	return copyBufPool.Get().(*[copyBufPoolSize]byte)[:]
   824  }
   825  func putCopyBuf(b []byte) {
   826  	if len(b) != copyBufPoolSize {
   827  		panic("trying to put back buffer of the wrong size in the copyBufPool")
   828  	}
   829  	copyBufPool.Put((*[copyBufPoolSize]byte)(b))
   830  }
   831  
   832  func bufioWriterPool(size int) *sync.Pool {
   833  	switch size {
   834  	case 2 << 10:
   835  		return &bufioWriter2kPool
   836  	case 4 << 10:
   837  		return &bufioWriter4kPool
   838  	}
   839  	return nil
   840  }
   841  
   842  // newBufioReader should be an internal detail,
   843  // but widely used packages access it using linkname.
   844  // Notable members of the hall of shame include:
   845  //   - github.com/gobwas/ws
   846  //
   847  // Do not remove or change the type signature.
   848  // See go.dev/issue/67401.
   849  //
   850  //go:linkname newBufioReader
   851  func newBufioReader(r io.Reader) *bufio.Reader {
   852  	if v := bufioReaderPool.Get(); v != nil {
   853  		br := v.(*bufio.Reader)
   854  		br.Reset(r)
   855  		return br
   856  	}
   857  	// Note: if this reader size is ever changed, update
   858  	// TestHandlerBodyClose's assumptions.
   859  	return bufio.NewReader(r)
   860  }
   861  
   862  // putBufioReader should be an internal detail,
   863  // but widely used packages access it using linkname.
   864  // Notable members of the hall of shame include:
   865  //   - github.com/gobwas/ws
   866  //
   867  // Do not remove or change the type signature.
   868  // See go.dev/issue/67401.
   869  //
   870  //go:linkname putBufioReader
   871  func putBufioReader(br *bufio.Reader) {
   872  	br.Reset(nil)
   873  	bufioReaderPool.Put(br)
   874  }
   875  
   876  // newBufioWriterSize should be an internal detail,
   877  // but widely used packages access it using linkname.
   878  // Notable members of the hall of shame include:
   879  //   - github.com/gobwas/ws
   880  //
   881  // Do not remove or change the type signature.
   882  // See go.dev/issue/67401.
   883  //
   884  //go:linkname newBufioWriterSize
   885  func newBufioWriterSize(w io.Writer, size int) *bufio.Writer {
   886  	pool := bufioWriterPool(size)
   887  	if pool != nil {
   888  		if v := pool.Get(); v != nil {
   889  			bw := v.(*bufio.Writer)
   890  			bw.Reset(w)
   891  			return bw
   892  		}
   893  	}
   894  	return bufio.NewWriterSize(w, size)
   895  }
   896  
   897  // putBufioWriter should be an internal detail,
   898  // but widely used packages access it using linkname.
   899  // Notable members of the hall of shame include:
   900  //   - github.com/gobwas/ws
   901  //
   902  // Do not remove or change the type signature.
   903  // See go.dev/issue/67401.
   904  //
   905  //go:linkname putBufioWriter
   906  func putBufioWriter(bw *bufio.Writer) {
   907  	bw.Reset(nil)
   908  	if pool := bufioWriterPool(bw.Available()); pool != nil {
   909  		pool.Put(bw)
   910  	}
   911  }
   912  
   913  // DefaultMaxHeaderBytes is the maximum permitted size of the headers
   914  // in an HTTP request.
   915  // This can be overridden by setting [Server.MaxHeaderBytes].
   916  const DefaultMaxHeaderBytes = 1 << 20 // 1 MB
   917  
   918  func (s *Server) maxHeaderBytes() int {
   919  	if s.MaxHeaderBytes > 0 {
   920  		return s.MaxHeaderBytes
   921  	}
   922  	return DefaultMaxHeaderBytes
   923  }
   924  
   925  func (s *Server) initialReadLimitSize() int64 {
   926  	return int64(s.maxHeaderBytes()) + 4096 // bufio slop
   927  }
   928  
   929  // tlsHandshakeTimeout returns the time limit permitted for the TLS
   930  // handshake, or zero for unlimited.
   931  //
   932  // It returns the minimum of any positive ReadHeaderTimeout,
   933  // ReadTimeout, or WriteTimeout.
   934  func (s *Server) tlsHandshakeTimeout() time.Duration {
   935  	var ret time.Duration
   936  	for _, v := range [...]time.Duration{
   937  		s.ReadHeaderTimeout,
   938  		s.ReadTimeout,
   939  		s.WriteTimeout,
   940  	} {
   941  		if v <= 0 {
   942  			continue
   943  		}
   944  		if ret == 0 || v < ret {
   945  			ret = v
   946  		}
   947  	}
   948  	return ret
   949  }
   950  
   951  // wrapper around io.ReadCloser which on first read, sends an
   952  // HTTP/1.1 100 Continue header
   953  type expectContinueReader struct {
   954  	resp       *response
   955  	readCloser io.ReadCloser
   956  	closed     atomic.Bool
   957  	sawEOF     atomic.Bool
   958  }
   959  
   960  func (ecr *expectContinueReader) Read(p []byte) (n int, err error) {
   961  	if ecr.closed.Load() {
   962  		return 0, ErrBodyReadAfterClose
   963  	}
   964  	w := ecr.resp
   965  	if w.canWriteContinue.Load() {
   966  		w.writeContinueMu.Lock()
   967  		if w.canWriteContinue.Load() {
   968  			w.conn.bufw.WriteString("HTTP/1.1 100 Continue\r\n\r\n")
   969  			w.conn.bufw.Flush()
   970  			w.canWriteContinue.Store(false)
   971  		}
   972  		w.writeContinueMu.Unlock()
   973  	}
   974  	n, err = ecr.readCloser.Read(p)
   975  	if err == io.EOF {
   976  		ecr.sawEOF.Store(true)
   977  	}
   978  	return
   979  }
   980  
   981  func (ecr *expectContinueReader) Close() error {
   982  	ecr.closed.Store(true)
   983  	return ecr.readCloser.Close()
   984  }
   985  
   986  // TimeFormat is the time format to use when generating times in HTTP
   987  // headers. It is like [time.RFC1123] but hard-codes GMT as the time
   988  // zone. The time being formatted must be in UTC for Format to
   989  // generate the correct format.
   990  //
   991  // For parsing this time format, see [ParseTime].
   992  const TimeFormat = "Mon, 02 Jan 2006 15:04:05 GMT"
   993  
   994  var errTooLarge = errors.New("http: request too large")
   995  
   996  // Read next request from connection.
   997  func (c *conn) readRequest(ctx context.Context) (w *response, err error) {
   998  	if c.hijacked() {
   999  		return nil, ErrHijacked
  1000  	}
  1001  
  1002  	var (
  1003  		wholeReqDeadline time.Time // or zero if none
  1004  		hdrDeadline      time.Time // or zero if none
  1005  	)
  1006  	t0 := time.Now()
  1007  	if d := c.server.readHeaderTimeout(); d > 0 {
  1008  		hdrDeadline = t0.Add(d)
  1009  	}
  1010  	if d := c.server.ReadTimeout; d > 0 {
  1011  		wholeReqDeadline = t0.Add(d)
  1012  	}
  1013  	c.rwc.SetReadDeadline(hdrDeadline)
  1014  	if d := c.server.WriteTimeout; d > 0 {
  1015  		defer func() {
  1016  			c.rwc.SetWriteDeadline(time.Now().Add(d))
  1017  		}()
  1018  	}
  1019  
  1020  	c.r.setReadLimit(c.server.initialReadLimitSize())
  1021  	if c.lastMethod == "POST" {
  1022  		// RFC 7230 section 3 tolerance for old buggy clients.
  1023  		peek, _ := c.bufr.Peek(4) // ReadRequest will get err below
  1024  		c.bufr.Discard(numLeadingCRorLF(peek))
  1025  	}
  1026  	req, err := readRequest(c.bufr)
  1027  	if err != nil {
  1028  		if c.r.hitReadLimit() {
  1029  			return nil, errTooLarge
  1030  		}
  1031  		return nil, err
  1032  	}
  1033  
  1034  	if !http1ServerSupportsRequest(req) {
  1035  		return nil, statusError{StatusHTTPVersionNotSupported, "unsupported protocol version"}
  1036  	}
  1037  
  1038  	c.lastMethod = req.Method
  1039  	c.r.setInfiniteReadLimit()
  1040  
  1041  	hosts, haveHost := req.Header["Host"]
  1042  	isH2Upgrade := req.isH2Upgrade()
  1043  	if req.ProtoAtLeast(1, 1) && (!haveHost || len(hosts) == 0) && !isH2Upgrade && req.Method != "CONNECT" {
  1044  		return nil, badRequestError("missing required Host header")
  1045  	}
  1046  	if len(hosts) == 1 && !httpguts.ValidHostHeader(hosts[0]) {
  1047  		return nil, badRequestError("malformed Host header")
  1048  	}
  1049  	for k, vv := range req.Header {
  1050  		if !httpguts.ValidHeaderFieldName(k) {
  1051  			return nil, badRequestError("invalid header name")
  1052  		}
  1053  		for _, v := range vv {
  1054  			if !httpguts.ValidHeaderFieldValue(v) {
  1055  				return nil, badRequestError("invalid header value")
  1056  			}
  1057  		}
  1058  	}
  1059  	delete(req.Header, "Host")
  1060  
  1061  	ctx, cancelCtx := context.WithCancel(ctx)
  1062  	req.ctx = ctx
  1063  	req.RemoteAddr = c.remoteAddr
  1064  	req.TLS = c.tlsState
  1065  	if body, ok := req.Body.(*body); ok {
  1066  		body.doEarlyClose = true
  1067  	}
  1068  
  1069  	// Adjust the read deadline if necessary.
  1070  	if !hdrDeadline.Equal(wholeReqDeadline) {
  1071  		c.rwc.SetReadDeadline(wholeReqDeadline)
  1072  	}
  1073  
  1074  	w = &response{
  1075  		conn:          c,
  1076  		cancelCtx:     cancelCtx,
  1077  		req:           req,
  1078  		reqBody:       req.Body,
  1079  		handlerHeader: make(Header),
  1080  		contentLength: -1,
  1081  
  1082  		// We populate these ahead of time so we're not
  1083  		// reading from req.Header after their Handler starts
  1084  		// and maybe mutates it (Issue 14940)
  1085  		wants10KeepAlive: req.wantsHttp10KeepAlive(),
  1086  		wantsClose:       req.wantsClose(),
  1087  	}
  1088  	if isH2Upgrade {
  1089  		w.closeAfterReply = true
  1090  	}
  1091  	w.cw.res = w
  1092  	w.w = newBufioWriterSize(&w.cw, bufferBeforeChunkingSize)
  1093  	return w, nil
  1094  }
  1095  
  1096  // http1ServerSupportsRequest reports whether Go's HTTP/1.x server
  1097  // supports the given request.
  1098  func http1ServerSupportsRequest(req *Request) bool {
  1099  	if req.ProtoMajor == 1 {
  1100  		return true
  1101  	}
  1102  	// Accept "PRI * HTTP/2.0" upgrade requests, so Handlers can
  1103  	// wire up their own HTTP/2 upgrades.
  1104  	if req.ProtoMajor == 2 && req.ProtoMinor == 0 &&
  1105  		req.Method == "PRI" && req.RequestURI == "*" {
  1106  		return true
  1107  	}
  1108  	// Reject HTTP/0.x, and all other HTTP/2+ requests (which
  1109  	// aren't encoded in ASCII anyway).
  1110  	return false
  1111  }
  1112  
  1113  func (w *response) Header() Header {
  1114  	if w.cw.header == nil && w.wroteHeader && !w.cw.wroteHeader {
  1115  		// Accessing the header between logically writing it
  1116  		// and physically writing it means we need to allocate
  1117  		// a clone to snapshot the logically written state.
  1118  		w.cw.header = w.handlerHeader.Clone()
  1119  	}
  1120  	w.calledHeader = true
  1121  	return w.handlerHeader
  1122  }
  1123  
  1124  // maxPostHandlerReadBytes is the max number of Request.Body bytes not
  1125  // consumed by a handler that the server will read from the client
  1126  // in order to keep a connection alive. If there are more bytes
  1127  // than this, the server, to be paranoid, instead sends a
  1128  // "Connection close" response.
  1129  //
  1130  // This number is approximately what a typical machine's TCP buffer
  1131  // size is anyway.  (if we have the bytes on the machine, we might as
  1132  // well read them)
  1133  const maxPostHandlerReadBytes = 256 << 10
  1134  
  1135  func checkWriteHeaderCode(code int) {
  1136  	// Issue 22880: require valid WriteHeader status codes.
  1137  	// For now we only enforce that it's three digits.
  1138  	// In the future we might block things over 599 (600 and above aren't defined
  1139  	// at https://httpwg.org/specs/rfc7231.html#status.codes).
  1140  	// But for now any three digits.
  1141  	//
  1142  	// We used to send "HTTP/1.1 000 0" on the wire in responses but there's
  1143  	// no equivalent bogus thing we can realistically send in HTTP/2,
  1144  	// so we'll consistently panic instead and help people find their bugs
  1145  	// early. (We can't return an error from WriteHeader even if we wanted to.)
  1146  	if code < 100 || code > 999 {
  1147  		panic(fmt.Sprintf("invalid WriteHeader code %v", code))
  1148  	}
  1149  }
  1150  
  1151  // relevantCaller searches the call stack for the first function outside of net/http.
  1152  // The purpose of this function is to provide more helpful error messages.
  1153  func relevantCaller() runtime.Frame {
  1154  	pc := make([]uintptr, 16)
  1155  	n := runtime.Callers(1, pc)
  1156  	frames := runtime.CallersFrames(pc[:n])
  1157  	var frame runtime.Frame
  1158  	for {
  1159  		frame, more := frames.Next()
  1160  		if !strings.HasPrefix(frame.Function, "net/http.") {
  1161  			return frame
  1162  		}
  1163  		if !more {
  1164  			break
  1165  		}
  1166  	}
  1167  	return frame
  1168  }
  1169  
  1170  func (w *response) WriteHeader(code int) {
  1171  	if w.conn.hijacked() {
  1172  		caller := relevantCaller()
  1173  		w.conn.server.logf("http: response.WriteHeader on hijacked connection from %s (%s:%d)", caller.Function, path.Base(caller.File), caller.Line)
  1174  		return
  1175  	}
  1176  	if w.wroteHeader {
  1177  		caller := relevantCaller()
  1178  		w.conn.server.logf("http: superfluous response.WriteHeader call from %s (%s:%d)", caller.Function, path.Base(caller.File), caller.Line)
  1179  		return
  1180  	}
  1181  	checkWriteHeaderCode(code)
  1182  
  1183  	if code < 101 || code > 199 {
  1184  		// Sending a 100 Continue or any non-1xx header disables the
  1185  		// automatically-sent 100 Continue from Request.Body.Read.
  1186  		w.disableWriteContinue()
  1187  	}
  1188  
  1189  	// Handle informational headers.
  1190  	//
  1191  	// We shouldn't send any further headers after 101 Switching Protocols,
  1192  	// so it takes the non-informational path.
  1193  	if code >= 100 && code <= 199 && code != StatusSwitchingProtocols {
  1194  		writeStatusLine(w.conn.bufw, w.req.ProtoAtLeast(1, 1), code, w.statusBuf[:])
  1195  
  1196  		// Per RFC 8297 we must not clear the current header map
  1197  		w.handlerHeader.WriteSubset(w.conn.bufw, excludedHeadersNoBody)
  1198  		w.conn.bufw.Write(crlf)
  1199  		w.conn.bufw.Flush()
  1200  
  1201  		return
  1202  	}
  1203  
  1204  	w.wroteHeader = true
  1205  	w.status = code
  1206  
  1207  	if w.calledHeader && w.cw.header == nil {
  1208  		w.cw.header = w.handlerHeader.Clone()
  1209  	}
  1210  
  1211  	if cl := w.handlerHeader.get("Content-Length"); cl != "" {
  1212  		v, err := strconv.ParseInt(cl, 10, 64)
  1213  		if err == nil && v >= 0 {
  1214  			w.contentLength = v
  1215  		} else {
  1216  			w.conn.server.logf("http: invalid Content-Length of %q", cl)
  1217  			w.handlerHeader.Del("Content-Length")
  1218  		}
  1219  	}
  1220  }
  1221  
  1222  // extraHeader is the set of headers sometimes added by chunkWriter.writeHeader.
  1223  // This type is used to avoid extra allocations from cloning and/or populating
  1224  // the response Header map and all its 1-element slices.
  1225  type extraHeader struct {
  1226  	contentType      string
  1227  	connection       string
  1228  	transferEncoding string
  1229  	date             []byte // written if not nil
  1230  	contentLength    []byte // written if not nil
  1231  }
  1232  
  1233  // Sorted the same as extraHeader.Write's loop.
  1234  var extraHeaderKeys = [][]byte{
  1235  	[]byte("Content-Type"),
  1236  	[]byte("Connection"),
  1237  	[]byte("Transfer-Encoding"),
  1238  }
  1239  
  1240  var (
  1241  	headerContentLength = []byte("Content-Length: ")
  1242  	headerDate          = []byte("Date: ")
  1243  )
  1244  
  1245  // Write writes the headers described in h to w.
  1246  //
  1247  // This method has a value receiver, despite the somewhat large size
  1248  // of h, because it prevents an allocation. The escape analysis isn't
  1249  // smart enough to realize this function doesn't mutate h.
  1250  func (h extraHeader) Write(w *bufio.Writer) {
  1251  	if h.date != nil {
  1252  		w.Write(headerDate)
  1253  		w.Write(h.date)
  1254  		w.Write(crlf)
  1255  	}
  1256  	if h.contentLength != nil {
  1257  		w.Write(headerContentLength)
  1258  		w.Write(h.contentLength)
  1259  		w.Write(crlf)
  1260  	}
  1261  	for i, v := range []string{h.contentType, h.connection, h.transferEncoding} {
  1262  		if v != "" {
  1263  			w.Write(extraHeaderKeys[i])
  1264  			w.Write(colonSpace)
  1265  			w.WriteString(v)
  1266  			w.Write(crlf)
  1267  		}
  1268  	}
  1269  }
  1270  
  1271  // writeHeader finalizes the header sent to the client and writes it
  1272  // to cw.res.conn.bufw.
  1273  //
  1274  // p is not written by writeHeader, but is the first chunk of the body
  1275  // that will be written. It is sniffed for a Content-Type if none is
  1276  // set explicitly. It's also used to set the Content-Length, if the
  1277  // total body size was small and the handler has already finished
  1278  // running.
  1279  func (cw *chunkWriter) writeHeader(p []byte) {
  1280  	if cw.wroteHeader {
  1281  		return
  1282  	}
  1283  	cw.wroteHeader = true
  1284  
  1285  	w := cw.res
  1286  	keepAlivesEnabled := w.conn.server.doKeepAlives()
  1287  	isHEAD := w.req.Method == "HEAD"
  1288  
  1289  	// header is written out to w.conn.buf below. Depending on the
  1290  	// state of the handler, we either own the map or not. If we
  1291  	// don't own it, the exclude map is created lazily for
  1292  	// WriteSubset to remove headers. The setHeader struct holds
  1293  	// headers we need to add.
  1294  	header := cw.header
  1295  	owned := header != nil
  1296  	if !owned {
  1297  		header = w.handlerHeader
  1298  	}
  1299  	var excludeHeader map[string]bool
  1300  	delHeader := func(key string) {
  1301  		if owned {
  1302  			header.Del(key)
  1303  			return
  1304  		}
  1305  		if _, ok := header[key]; !ok {
  1306  			return
  1307  		}
  1308  		if excludeHeader == nil {
  1309  			excludeHeader = make(map[string]bool)
  1310  		}
  1311  		excludeHeader[key] = true
  1312  	}
  1313  	var setHeader extraHeader
  1314  
  1315  	// Don't write out the fake "Trailer:foo" keys. See TrailerPrefix.
  1316  	trailers := false
  1317  	for k := range cw.header {
  1318  		if strings.HasPrefix(k, TrailerPrefix) {
  1319  			if excludeHeader == nil {
  1320  				excludeHeader = make(map[string]bool)
  1321  			}
  1322  			excludeHeader[k] = true
  1323  			trailers = true
  1324  		}
  1325  	}
  1326  	for _, v := range cw.header["Trailer"] {
  1327  		trailers = true
  1328  		foreachHeaderElement(v, cw.res.declareTrailer)
  1329  	}
  1330  
  1331  	te := header.get("Transfer-Encoding")
  1332  	hasTE := te != ""
  1333  
  1334  	// If the handler is done but never sent a Content-Length
  1335  	// response header and this is our first (and last) write, set
  1336  	// it, even to zero. This helps HTTP/1.0 clients keep their
  1337  	// "keep-alive" connections alive.
  1338  	// Exceptions: 304/204/1xx responses never get Content-Length, and if
  1339  	// it was a HEAD request, we don't know the difference between
  1340  	// 0 actual bytes and 0 bytes because the handler noticed it
  1341  	// was a HEAD request and chose not to write anything. So for
  1342  	// HEAD, the handler should either write the Content-Length or
  1343  	// write non-zero bytes. If it's actually 0 bytes and the
  1344  	// handler never looked at the Request.Method, we just don't
  1345  	// send a Content-Length header.
  1346  	// Further, we don't send an automatic Content-Length if they
  1347  	// set a Transfer-Encoding, because they're generally incompatible.
  1348  	if w.handlerDone.Load() && !trailers && !hasTE && bodyAllowedForStatus(w.status) && !header.has("Content-Length") && (!isHEAD || len(p) > 0) {
  1349  		w.contentLength = int64(len(p))
  1350  		setHeader.contentLength = strconv.AppendInt(cw.res.clenBuf[:0], int64(len(p)), 10)
  1351  	}
  1352  
  1353  	// If this was an HTTP/1.0 request with keep-alive and we sent a
  1354  	// Content-Length back, we can make this a keep-alive response ...
  1355  	if w.wants10KeepAlive && keepAlivesEnabled {
  1356  		sentLength := header.get("Content-Length") != ""
  1357  		if sentLength && header.get("Connection") == "keep-alive" {
  1358  			w.closeAfterReply = false
  1359  		}
  1360  	}
  1361  
  1362  	// Check for an explicit (and valid) Content-Length header.
  1363  	hasCL := w.contentLength != -1
  1364  
  1365  	if w.wants10KeepAlive && (isHEAD || hasCL || !bodyAllowedForStatus(w.status)) {
  1366  		_, connectionHeaderSet := header["Connection"]
  1367  		if !connectionHeaderSet {
  1368  			setHeader.connection = "keep-alive"
  1369  		}
  1370  	} else if !w.req.ProtoAtLeast(1, 1) || w.wantsClose {
  1371  		w.closeAfterReply = true
  1372  	}
  1373  
  1374  	if header.get("Connection") == "close" || !keepAlivesEnabled {
  1375  		w.closeAfterReply = true
  1376  	}
  1377  
  1378  	// If the client wanted a 100-continue but we never sent it to
  1379  	// them (or, more strictly: we never finished reading their
  1380  	// request body), don't reuse this connection.
  1381  	//
  1382  	// This behavior was first added on the theory that we don't know
  1383  	// if the next bytes on the wire are going to be the remainder of
  1384  	// the request body or the subsequent request (see issue 11549),
  1385  	// but that's not correct: If we keep using the connection,
  1386  	// the client is required to send the request body whether we
  1387  	// asked for it or not.
  1388  	//
  1389  	// We probably do want to skip reusing the connection in most cases,
  1390  	// however. If the client is offering a large request body that we
  1391  	// don't intend to use, then it's better to close the connection
  1392  	// than to read the body. For now, assume that if we're sending
  1393  	// headers, the handler is done reading the body and we should
  1394  	// drop the connection if we haven't seen EOF.
  1395  	if ecr, ok := w.req.Body.(*expectContinueReader); ok && !ecr.sawEOF.Load() {
  1396  		w.closeAfterReply = true
  1397  	}
  1398  
  1399  	// We do this by default because there are a number of clients that
  1400  	// send a full request before starting to read the response, and they
  1401  	// can deadlock if we start writing the response with unconsumed body
  1402  	// remaining. See Issue 15527 for some history.
  1403  	//
  1404  	// If full duplex mode has been enabled with ResponseController.EnableFullDuplex,
  1405  	// then leave the request body alone.
  1406  	//
  1407  	// We don't take this path when w.closeAfterReply is set.
  1408  	// We may not need to consume the request to get ready for the next one
  1409  	// (since we're closing the conn), but a client which sends a full request
  1410  	// before reading a response may deadlock in this case.
  1411  	// This behavior has been present since CL 5268043 (2011), however,
  1412  	// so it doesn't seem to be causing problems.
  1413  	if w.req.ContentLength != 0 && !w.closeAfterReply && !w.fullDuplex {
  1414  		var discard, tooBig bool
  1415  
  1416  		switch bdy := w.req.Body.(type) {
  1417  		case *expectContinueReader:
  1418  			// We only get here if we have already fully consumed the request body
  1419  			// (see above).
  1420  		case *body:
  1421  			bdy.mu.Lock()
  1422  			switch {
  1423  			case bdy.closed:
  1424  				if !bdy.sawEOF {
  1425  					// Body was closed in handler with non-EOF error.
  1426  					w.closeAfterReply = true
  1427  				}
  1428  			case bdy.unreadDataSizeLocked() >= maxPostHandlerReadBytes:
  1429  				tooBig = true
  1430  			default:
  1431  				discard = true
  1432  			}
  1433  			bdy.mu.Unlock()
  1434  		default:
  1435  			discard = true
  1436  		}
  1437  
  1438  		if discard {
  1439  			_, err := io.CopyN(io.Discard, w.reqBody, maxPostHandlerReadBytes+1)
  1440  			switch err {
  1441  			case nil:
  1442  				// There must be even more data left over.
  1443  				tooBig = true
  1444  			case ErrBodyReadAfterClose:
  1445  				// Body was already consumed and closed.
  1446  			case io.EOF:
  1447  				// The remaining body was just consumed, close it.
  1448  				err = w.reqBody.Close()
  1449  				if err != nil {
  1450  					w.closeAfterReply = true
  1451  				}
  1452  			default:
  1453  				// Some other kind of error occurred, like a read timeout, or
  1454  				// corrupt chunked encoding. In any case, whatever remains
  1455  				// on the wire must not be parsed as another HTTP request.
  1456  				w.closeAfterReply = true
  1457  			}
  1458  		}
  1459  
  1460  		if tooBig {
  1461  			w.requestTooLarge()
  1462  			delHeader("Connection")
  1463  			setHeader.connection = "close"
  1464  		}
  1465  	}
  1466  
  1467  	code := w.status
  1468  	if bodyAllowedForStatus(code) {
  1469  		// If no content type, apply sniffing algorithm to body.
  1470  		_, haveType := header["Content-Type"]
  1471  
  1472  		// If the Content-Encoding was set and is non-blank,
  1473  		// we shouldn't sniff the body. See Issue 31753.
  1474  		ce := header.Get("Content-Encoding")
  1475  		hasCE := len(ce) > 0
  1476  		if !hasCE && !haveType && !hasTE && len(p) > 0 {
  1477  			setHeader.contentType = DetectContentType(p)
  1478  		}
  1479  	} else {
  1480  		for _, k := range suppressedHeaders(code) {
  1481  			delHeader(k)
  1482  		}
  1483  	}
  1484  
  1485  	if !header.has("Date") {
  1486  		setHeader.date = time.Now().UTC().AppendFormat(cw.res.dateBuf[:0], TimeFormat)
  1487  	}
  1488  
  1489  	if hasCL && hasTE && te != "identity" {
  1490  		// TODO: return an error if WriteHeader gets a return parameter
  1491  		// For now just ignore the Content-Length.
  1492  		w.conn.server.logf("http: WriteHeader called with both Transfer-Encoding of %q and a Content-Length of %d",
  1493  			te, w.contentLength)
  1494  		delHeader("Content-Length")
  1495  		hasCL = false
  1496  	}
  1497  
  1498  	if w.req.Method == "HEAD" || !bodyAllowedForStatus(code) || code == StatusNoContent {
  1499  		// Response has no body.
  1500  		delHeader("Transfer-Encoding")
  1501  	} else if hasCL {
  1502  		// Content-Length has been provided, so no chunking is to be done.
  1503  		delHeader("Transfer-Encoding")
  1504  	} else if w.req.ProtoAtLeast(1, 1) {
  1505  		// HTTP/1.1 or greater: Transfer-Encoding has been set to identity, and no
  1506  		// content-length has been provided. The connection must be closed after the
  1507  		// reply is written, and no chunking is to be done. This is the setup
  1508  		// recommended in the Server-Sent Events candidate recommendation 11,
  1509  		// section 8.
  1510  		if hasTE && te == "identity" {
  1511  			cw.chunking = false
  1512  			w.closeAfterReply = true
  1513  			delHeader("Transfer-Encoding")
  1514  		} else {
  1515  			// HTTP/1.1 or greater: use chunked transfer encoding
  1516  			// to avoid closing the connection at EOF.
  1517  			cw.chunking = true
  1518  			setHeader.transferEncoding = "chunked"
  1519  			if hasTE && te == "chunked" {
  1520  				// We will send the chunked Transfer-Encoding header later.
  1521  				delHeader("Transfer-Encoding")
  1522  			}
  1523  		}
  1524  	} else {
  1525  		// HTTP version < 1.1: cannot do chunked transfer
  1526  		// encoding and we don't know the Content-Length so
  1527  		// signal EOF by closing connection.
  1528  		w.closeAfterReply = true
  1529  		delHeader("Transfer-Encoding") // in case already set
  1530  	}
  1531  
  1532  	// Cannot use Content-Length with non-identity Transfer-Encoding.
  1533  	if cw.chunking {
  1534  		delHeader("Content-Length")
  1535  	}
  1536  	if !w.req.ProtoAtLeast(1, 0) {
  1537  		return
  1538  	}
  1539  
  1540  	// Only override the Connection header if it is not a successful
  1541  	// protocol switch response and if KeepAlives are not enabled.
  1542  	// See https://golang.org/issue/36381.
  1543  	delConnectionHeader := w.closeAfterReply &&
  1544  		(!keepAlivesEnabled || !hasToken(cw.header.get("Connection"), "close")) &&
  1545  		!isProtocolSwitchResponse(w.status, header)
  1546  	if delConnectionHeader {
  1547  		delHeader("Connection")
  1548  		if w.req.ProtoAtLeast(1, 1) {
  1549  			setHeader.connection = "close"
  1550  		}
  1551  	}
  1552  
  1553  	writeStatusLine(w.conn.bufw, w.req.ProtoAtLeast(1, 1), code, w.statusBuf[:])
  1554  	cw.header.WriteSubset(w.conn.bufw, excludeHeader)
  1555  	setHeader.Write(w.conn.bufw)
  1556  	w.conn.bufw.Write(crlf)
  1557  }
  1558  
  1559  // foreachHeaderElement splits v according to the "#rule" construction
  1560  // in RFC 7230 section 7 and calls fn for each non-empty element.
  1561  func foreachHeaderElement(v string, fn func(string)) {
  1562  	v = textproto.TrimString(v)
  1563  	if v == "" {
  1564  		return
  1565  	}
  1566  	if !strings.Contains(v, ",") {
  1567  		fn(v)
  1568  		return
  1569  	}
  1570  	for f := range strings.SplitSeq(v, ",") {
  1571  		if f = textproto.TrimString(f); f != "" {
  1572  			fn(f)
  1573  		}
  1574  	}
  1575  }
  1576  
  1577  // writeStatusLine writes an HTTP/1.x Status-Line (RFC 7230 Section 3.1.2)
  1578  // to bw. is11 is whether the HTTP request is HTTP/1.1. false means HTTP/1.0.
  1579  // code is the response status code.
  1580  // scratch is an optional scratch buffer. If it has at least capacity 3, it's used.
  1581  func writeStatusLine(bw *bufio.Writer, is11 bool, code int, scratch []byte) {
  1582  	if is11 {
  1583  		bw.WriteString("HTTP/1.1 ")
  1584  	} else {
  1585  		bw.WriteString("HTTP/1.0 ")
  1586  	}
  1587  	if text := StatusText(code); text != "" {
  1588  		bw.Write(strconv.AppendInt(scratch[:0], int64(code), 10))
  1589  		bw.WriteByte(' ')
  1590  		bw.WriteString(text)
  1591  		bw.WriteString("\r\n")
  1592  	} else {
  1593  		// don't worry about performance
  1594  		fmt.Fprintf(bw, "%03d status code %d\r\n", code, code)
  1595  	}
  1596  }
  1597  
  1598  // bodyAllowed reports whether a Write is allowed for this response type.
  1599  // It's illegal to call this before the header has been flushed.
  1600  func (w *response) bodyAllowed() bool {
  1601  	if !w.wroteHeader {
  1602  		panic("")
  1603  	}
  1604  	return bodyAllowedForStatus(w.status)
  1605  }
  1606  
  1607  // The Life Of A Write is like this:
  1608  //
  1609  // Handler starts. No header has been sent. The handler can either
  1610  // write a header, or just start writing. Writing before sending a header
  1611  // sends an implicitly empty 200 OK header.
  1612  //
  1613  // If the handler didn't declare a Content-Length up front, we either
  1614  // go into chunking mode or, if the handler finishes running before
  1615  // the chunking buffer size, we compute a Content-Length and send that
  1616  // in the header instead.
  1617  //
  1618  // Likewise, if the handler didn't set a Content-Type, we sniff that
  1619  // from the initial chunk of output.
  1620  //
  1621  // The Writers are wired together like:
  1622  //
  1623  //  1. *response (the ResponseWriter) ->
  1624  //  2. (*response).w, a [*bufio.Writer] of bufferBeforeChunkingSize bytes ->
  1625  //  3. chunkWriter.Writer (whose writeHeader finalizes Content-Length/Type)
  1626  //     and which writes the chunk headers, if needed ->
  1627  //  4. conn.bufw, a *bufio.Writer of default (4kB) bytes, writing to ->
  1628  //  5. checkConnErrorWriter{c}, which notes any non-nil error on Write
  1629  //     and populates c.werr with it if so, but otherwise writes to ->
  1630  //  6. the rwc, the [net.Conn].
  1631  //
  1632  // TODO(bradfitz): short-circuit some of the buffering when the
  1633  // initial header contains both a Content-Type and Content-Length.
  1634  // Also short-circuit in (1) when the header's been sent and not in
  1635  // chunking mode, writing directly to (4) instead, if (2) has no
  1636  // buffered data. More generally, we could short-circuit from (1) to
  1637  // (3) even in chunking mode if the write size from (1) is over some
  1638  // threshold and nothing is in (2).  The answer might be mostly making
  1639  // bufferBeforeChunkingSize smaller and having bufio's fast-paths deal
  1640  // with this instead.
  1641  func (w *response) Write(data []byte) (n int, err error) {
  1642  	return w.write(len(data), data, "")
  1643  }
  1644  
  1645  func (w *response) WriteString(data string) (n int, err error) {
  1646  	return w.write(len(data), nil, data)
  1647  }
  1648  
  1649  // either dataB or dataS is non-zero.
  1650  func (w *response) write(lenData int, dataB []byte, dataS string) (n int, err error) {
  1651  	if w.conn.hijacked() {
  1652  		if lenData > 0 {
  1653  			caller := relevantCaller()
  1654  			w.conn.server.logf("http: response.Write on hijacked connection from %s (%s:%d)", caller.Function, path.Base(caller.File), caller.Line)
  1655  		}
  1656  		return 0, ErrHijacked
  1657  	}
  1658  
  1659  	if w.canWriteContinue.Load() {
  1660  		// Body reader wants to write 100 Continue but hasn't yet. Tell it not to.
  1661  		w.disableWriteContinue()
  1662  	}
  1663  
  1664  	if !w.wroteHeader {
  1665  		w.WriteHeader(StatusOK)
  1666  	}
  1667  	if lenData == 0 {
  1668  		return 0, nil
  1669  	}
  1670  	if !w.bodyAllowed() {
  1671  		return 0, ErrBodyNotAllowed
  1672  	}
  1673  
  1674  	w.written += int64(lenData) // ignoring errors, for errorKludge
  1675  	if w.contentLength != -1 && w.written > w.contentLength {
  1676  		return 0, ErrContentLength
  1677  	}
  1678  	if dataB != nil {
  1679  		return w.w.Write(dataB)
  1680  	} else {
  1681  		return w.w.WriteString(dataS)
  1682  	}
  1683  }
  1684  
  1685  func (w *response) finishRequest() {
  1686  	w.handlerDone.Store(true)
  1687  
  1688  	if !w.wroteHeader {
  1689  		w.WriteHeader(StatusOK)
  1690  	}
  1691  
  1692  	w.w.Flush()
  1693  	putBufioWriter(w.w)
  1694  	w.cw.close()
  1695  	w.conn.bufw.Flush()
  1696  
  1697  	w.conn.r.abortPendingRead()
  1698  
  1699  	// Close the body (regardless of w.closeAfterReply) so we can
  1700  	// re-use its bufio.Reader later safely.
  1701  	w.reqBody.Close()
  1702  
  1703  	if w.req.MultipartForm != nil {
  1704  		w.req.MultipartForm.RemoveAll()
  1705  	}
  1706  }
  1707  
  1708  // shouldReuseConnection reports whether the underlying TCP connection can be reused.
  1709  // It must only be called after the handler is done executing.
  1710  func (w *response) shouldReuseConnection() bool {
  1711  	if w.closeAfterReply {
  1712  		// The request or something set while executing the
  1713  		// handler indicated we shouldn't reuse this
  1714  		// connection.
  1715  		return false
  1716  	}
  1717  
  1718  	if w.req.Method != "HEAD" && w.contentLength != -1 && w.bodyAllowed() && w.contentLength != w.written {
  1719  		// Did not write enough. Avoid getting out of sync.
  1720  		return false
  1721  	}
  1722  
  1723  	// There was some error writing to the underlying connection
  1724  	// during the request, so don't re-use this conn.
  1725  	if w.conn.werr != nil {
  1726  		return false
  1727  	}
  1728  
  1729  	if w.closedRequestBodyEarly() {
  1730  		return false
  1731  	}
  1732  
  1733  	return true
  1734  }
  1735  
  1736  func (w *response) closedRequestBodyEarly() bool {
  1737  	body, ok := w.req.Body.(*body)
  1738  	return ok && body.didEarlyClose()
  1739  }
  1740  
  1741  func (w *response) Flush() {
  1742  	w.FlushError()
  1743  }
  1744  
  1745  func (w *response) FlushError() error {
  1746  	if !w.wroteHeader {
  1747  		w.WriteHeader(StatusOK)
  1748  	}
  1749  	err := w.w.Flush()
  1750  	e2 := w.cw.flush()
  1751  	if err == nil {
  1752  		err = e2
  1753  	}
  1754  	return err
  1755  }
  1756  
  1757  func (c *conn) finalFlush() {
  1758  	if c.bufr != nil {
  1759  		// Steal the bufio.Reader (~4KB worth of memory) and its associated
  1760  		// reader for a future connection.
  1761  		putBufioReader(c.bufr)
  1762  		c.bufr = nil
  1763  	}
  1764  
  1765  	if c.bufw != nil {
  1766  		c.bufw.Flush()
  1767  		// Steal the bufio.Writer (~4KB worth of memory) and its associated
  1768  		// writer for a future connection.
  1769  		putBufioWriter(c.bufw)
  1770  		c.bufw = nil
  1771  	}
  1772  }
  1773  
  1774  // Close the connection.
  1775  func (c *conn) close() {
  1776  	c.finalFlush()
  1777  	c.rwc.Close()
  1778  }
  1779  
  1780  // rstAvoidanceDelay is the amount of time we sleep after closing the
  1781  // write side of a TCP connection before closing the entire socket.
  1782  // By sleeping, we increase the chances that the client sees our FIN
  1783  // and processes its final data before they process the subsequent RST
  1784  // from closing a connection with known unread data.
  1785  // This RST seems to occur mostly on BSD systems. (And Windows?)
  1786  // This timeout is somewhat arbitrary (~latency around the planet),
  1787  // and may be modified by tests.
  1788  //
  1789  // TODO(bcmills): This should arguably be a server configuration parameter,
  1790  // not a hard-coded value.
  1791  var rstAvoidanceDelay = 500 * time.Millisecond
  1792  
  1793  type closeWriter interface {
  1794  	CloseWrite() error
  1795  }
  1796  
  1797  var _ closeWriter = (*net.TCPConn)(nil)
  1798  
  1799  // closeWriteAndWait flushes any outstanding data and sends a FIN packet (if
  1800  // client is connected via TCP), signaling that we're done. We then
  1801  // pause for a bit, hoping the client processes it before any
  1802  // subsequent RST.
  1803  //
  1804  // See https://golang.org/issue/3595
  1805  func (c *conn) closeWriteAndWait() {
  1806  	c.finalFlush()
  1807  	if tcp, ok := c.rwc.(closeWriter); ok {
  1808  		tcp.CloseWrite()
  1809  	}
  1810  
  1811  	// When we return from closeWriteAndWait, the caller will fully close the
  1812  	// connection. If client is still writing to the connection, this will cause
  1813  	// the write to fail with ECONNRESET or similar. Unfortunately, many TCP
  1814  	// implementations will also drop unread packets from the client's read buffer
  1815  	// when a write fails, causing our final response to be truncated away too.
  1816  	//
  1817  	// As a result, https://www.rfc-editor.org/rfc/rfc7230#section-6.6 recommends
  1818  	// that “[t]he server … continues to read from the connection until it
  1819  	// receives a corresponding close by the client, or until the server is
  1820  	// reasonably certain that its own TCP stack has received the client's
  1821  	// acknowledgement of the packet(s) containing the server's last response.”
  1822  	//
  1823  	// Unfortunately, we have no straightforward way to be “reasonably certain”
  1824  	// that we have received the client's ACK, and at any rate we don't want to
  1825  	// allow a misbehaving client to soak up server connections indefinitely by
  1826  	// withholding an ACK, nor do we want to go through the complexity or overhead
  1827  	// of using low-level APIs to figure out when a TCP round-trip has completed.
  1828  	//
  1829  	// Instead, we declare that we are “reasonably certain” that we received the
  1830  	// ACK if maxRSTAvoidanceDelay has elapsed.
  1831  	time.Sleep(rstAvoidanceDelay)
  1832  }
  1833  
  1834  // validNextProto reports whether the proto is a valid ALPN protocol name.
  1835  // Everything is valid except the empty string and built-in protocol types,
  1836  // so that those can't be overridden with alternate implementations.
  1837  func validNextProto(proto string) bool {
  1838  	switch proto {
  1839  	case "", "http/1.1", "http/1.0":
  1840  		return false
  1841  	}
  1842  	return true
  1843  }
  1844  
  1845  const (
  1846  	runHooks  = true
  1847  	skipHooks = false
  1848  )
  1849  
  1850  func (c *conn) setState(nc net.Conn, state ConnState, runHook bool) {
  1851  	srv := c.server
  1852  	switch state {
  1853  	case StateNew:
  1854  		srv.trackConn(c, true)
  1855  	case StateHijacked, StateClosed:
  1856  		srv.trackConn(c, false)
  1857  	}
  1858  	if state > 0xff || state < 0 {
  1859  		panic("internal error")
  1860  	}
  1861  	packedState := uint64(time.Now().Unix()<<8) | uint64(state)
  1862  	c.curState.Store(packedState)
  1863  	if !runHook {
  1864  		return
  1865  	}
  1866  	if hook := srv.ConnState; hook != nil {
  1867  		hook(nc, state)
  1868  	}
  1869  }
  1870  
  1871  func (c *conn) getState() (state ConnState, unixSec int64) {
  1872  	packedState := c.curState.Load()
  1873  	return ConnState(packedState & 0xff), int64(packedState >> 8)
  1874  }
  1875  
  1876  // badRequestError is a literal string (used by in the server in HTML,
  1877  // unescaped) to tell the user why their request was bad. It should
  1878  // be plain text without user info or other embedded errors.
  1879  func badRequestError(e string) error { return statusError{StatusBadRequest, e} }
  1880  
  1881  // statusError is an error used to respond to a request with an HTTP status.
  1882  // The text should be plain text without user info or other embedded errors.
  1883  type statusError struct {
  1884  	code int
  1885  	text string
  1886  }
  1887  
  1888  func (e statusError) Error() string { return StatusText(e.code) + ": " + e.text }
  1889  
  1890  // ErrAbortHandler is a sentinel panic value to abort a handler.
  1891  // While any panic from ServeHTTP aborts the response to the client,
  1892  // panicking with ErrAbortHandler also suppresses logging of a stack
  1893  // trace to the server's error log.
  1894  var ErrAbortHandler = errors.New("net/http: abort Handler")
  1895  
  1896  // isCommonNetReadError reports whether err is a common error
  1897  // encountered during reading a request off the network when the
  1898  // client has gone away or had its read fail somehow. This is used to
  1899  // determine which logs are interesting enough to log about.
  1900  func isCommonNetReadError(err error) bool {
  1901  	if err == io.EOF {
  1902  		return true
  1903  	}
  1904  	if neterr, ok := err.(net.Error); ok && neterr.Timeout() {
  1905  		return true
  1906  	}
  1907  	if oe, ok := err.(*net.OpError); ok && oe.Op == "read" {
  1908  		return true
  1909  	}
  1910  	return false
  1911  }
  1912  
  1913  // Serve a new connection.
  1914  func (c *conn) serve(ctx context.Context) {
  1915  	if ra := c.rwc.RemoteAddr(); ra != nil {
  1916  		c.remoteAddr = ra.String()
  1917  	}
  1918  	ctx = context.WithValue(ctx, LocalAddrContextKey, c.rwc.LocalAddr())
  1919  	var inFlightResponse *response
  1920  	defer func() {
  1921  		if err := recover(); err != nil && err != ErrAbortHandler {
  1922  			const size = 64 << 10
  1923  			buf := make([]byte, size)
  1924  			buf = buf[:runtime.Stack(buf, false)]
  1925  			c.server.logf("http: panic serving %v: %v\n%s", c.remoteAddr, err, buf)
  1926  		}
  1927  		if inFlightResponse != nil {
  1928  			inFlightResponse.cancelCtx()
  1929  			inFlightResponse.disableWriteContinue()
  1930  		}
  1931  		if !c.hijacked() {
  1932  			if inFlightResponse != nil {
  1933  				inFlightResponse.conn.r.abortPendingRead()
  1934  				inFlightResponse.reqBody.Close()
  1935  			}
  1936  			c.close()
  1937  			c.setState(c.rwc, StateClosed, runHooks)
  1938  		}
  1939  	}()
  1940  
  1941  	if tlsConn, ok := c.rwc.(*tls.Conn); ok {
  1942  		tlsTO := c.server.tlsHandshakeTimeout()
  1943  		if tlsTO > 0 {
  1944  			dl := time.Now().Add(tlsTO)
  1945  			c.rwc.SetReadDeadline(dl)
  1946  			c.rwc.SetWriteDeadline(dl)
  1947  		}
  1948  		if err := tlsConn.HandshakeContext(ctx); err != nil {
  1949  			// If the handshake failed due to the client not speaking
  1950  			// TLS, assume they're speaking plaintext HTTP and write a
  1951  			// 400 response on the TLS conn's underlying net.Conn.
  1952  			var reason string
  1953  			if re, ok := err.(tls.RecordHeaderError); ok && re.Conn != nil && tlsRecordHeaderLooksLikeHTTP(re.RecordHeader) {
  1954  				io.WriteString(re.Conn, "HTTP/1.0 400 Bad Request\r\n\r\nClient sent an HTTP request to an HTTPS server.\n")
  1955  				re.Conn.Close()
  1956  				reason = "client sent an HTTP request to an HTTPS server"
  1957  			} else {
  1958  				reason = err.Error()
  1959  			}
  1960  			c.server.logf("http: TLS handshake error from %s: %v", c.rwc.RemoteAddr(), reason)
  1961  			return
  1962  		}
  1963  		// Restore Conn-level deadlines.
  1964  		if tlsTO > 0 {
  1965  			c.rwc.SetReadDeadline(time.Time{})
  1966  			c.rwc.SetWriteDeadline(time.Time{})
  1967  		}
  1968  		c.tlsState = new(tls.ConnectionState)
  1969  		*c.tlsState = tlsConn.ConnectionState()
  1970  		if proto := c.tlsState.NegotiatedProtocol; validNextProto(proto) {
  1971  			if fn := c.server.TLSNextProto[proto]; fn != nil {
  1972  				h := initALPNRequest{ctx, tlsConn, serverHandler{c.server}}
  1973  				// Mark freshly created HTTP/2 as active and prevent any server state hooks
  1974  				// from being run on these connections. This prevents closeIdleConns from
  1975  				// closing such connections. See issue https://golang.org/issue/39776.
  1976  				c.setState(c.rwc, StateActive, skipHooks)
  1977  				fn(c.server, tlsConn, h)
  1978  			}
  1979  			return
  1980  		}
  1981  	}
  1982  
  1983  	// HTTP/1.x from here on.
  1984  
  1985  	ctx, cancelCtx := context.WithCancel(ctx)
  1986  	c.cancelCtx = cancelCtx
  1987  	defer cancelCtx()
  1988  
  1989  	c.r = &connReader{conn: c}
  1990  	c.bufr = newBufioReader(c.r)
  1991  	c.bufw = newBufioWriterSize(checkConnErrorWriter{c}, 4<<10)
  1992  
  1993  	protos := c.server.protocols()
  1994  	if c.tlsState == nil && protos.UnencryptedHTTP2() {
  1995  		if c.maybeServeUnencryptedHTTP2(ctx) {
  1996  			return
  1997  		}
  1998  	}
  1999  	if !protos.HTTP1() {
  2000  		return
  2001  	}
  2002  
  2003  	for {
  2004  		w, err := c.readRequest(ctx)
  2005  		if c.r.remain != c.server.initialReadLimitSize() {
  2006  			// If we read any bytes off the wire, we're active.
  2007  			c.setState(c.rwc, StateActive, runHooks)
  2008  		}
  2009  		if c.server.shuttingDown() {
  2010  			return
  2011  		}
  2012  		if err != nil {
  2013  			const errorHeaders = "\r\nContent-Type: text/plain; charset=utf-8\r\nConnection: close\r\n\r\n"
  2014  
  2015  			switch {
  2016  			case err == errTooLarge:
  2017  				// Their HTTP client may or may not be
  2018  				// able to read this if we're
  2019  				// responding to them and hanging up
  2020  				// while they're still writing their
  2021  				// request. Undefined behavior.
  2022  				const publicErr = "431 Request Header Fields Too Large"
  2023  				fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr)
  2024  				c.closeWriteAndWait()
  2025  				return
  2026  
  2027  			case isUnsupportedTEError(err):
  2028  				// Respond as per RFC 7230 Section 3.3.1 which says,
  2029  				//      A server that receives a request message with a
  2030  				//      transfer coding it does not understand SHOULD
  2031  				//      respond with 501 (Unimplemented).
  2032  				code := StatusNotImplemented
  2033  
  2034  				// We purposefully aren't echoing back the transfer-encoding's value,
  2035  				// so as to mitigate the risk of cross side scripting by an attacker.
  2036  				fmt.Fprintf(c.rwc, "HTTP/1.1 %d %s%sUnsupported transfer encoding", code, StatusText(code), errorHeaders)
  2037  				return
  2038  
  2039  			case isCommonNetReadError(err):
  2040  				return // don't reply
  2041  
  2042  			default:
  2043  				if v, ok := err.(statusError); ok {
  2044  					fmt.Fprintf(c.rwc, "HTTP/1.1 %d %s: %s%s%d %s: %s", v.code, StatusText(v.code), v.text, errorHeaders, v.code, StatusText(v.code), v.text)
  2045  					return
  2046  				}
  2047  				const publicErr = "400 Bad Request"
  2048  				fmt.Fprintf(c.rwc, "HTTP/1.1 "+publicErr+errorHeaders+publicErr)
  2049  				return
  2050  			}
  2051  		}
  2052  
  2053  		// Expect 100 Continue support
  2054  		req := w.req
  2055  		if req.expectsContinue() {
  2056  			if req.ProtoAtLeast(1, 1) && req.ContentLength != 0 {
  2057  				// Wrap the Body reader with one that replies on the connection
  2058  				req.Body = &expectContinueReader{readCloser: req.Body, resp: w}
  2059  				w.canWriteContinue.Store(true)
  2060  			}
  2061  		} else if req.Header.get("Expect") != "" {
  2062  			w.sendExpectationFailed()
  2063  			return
  2064  		}
  2065  
  2066  		c.curReq.Store(w)
  2067  
  2068  		if requestBodyRemains(req.Body) {
  2069  			registerOnHitEOF(req.Body, w.conn.r.startBackgroundRead)
  2070  		} else {
  2071  			w.conn.r.startBackgroundRead()
  2072  		}
  2073  
  2074  		// HTTP cannot have multiple simultaneous active requests.[*]
  2075  		// Until the server replies to this request, it can't read another,
  2076  		// so we might as well run the handler in this goroutine.
  2077  		// [*] Not strictly true: HTTP pipelining. We could let them all process
  2078  		// in parallel even if their responses need to be serialized.
  2079  		// But we're not going to implement HTTP pipelining because it
  2080  		// was never deployed in the wild and the answer is HTTP/2.
  2081  		inFlightResponse = w
  2082  		serverHandler{c.server}.ServeHTTP(w, w.req)
  2083  		inFlightResponse = nil
  2084  		w.cancelCtx()
  2085  		if c.hijacked() {
  2086  			return
  2087  		}
  2088  		w.finishRequest()
  2089  		c.rwc.SetWriteDeadline(time.Time{})
  2090  		if !w.shouldReuseConnection() {
  2091  			if w.requestBodyLimitHit || w.closedRequestBodyEarly() {
  2092  				c.closeWriteAndWait()
  2093  			}
  2094  			return
  2095  		}
  2096  		c.setState(c.rwc, StateIdle, runHooks)
  2097  		c.curReq.Store(nil)
  2098  
  2099  		if !w.conn.server.doKeepAlives() {
  2100  			// We're in shutdown mode. We might've replied
  2101  			// to the user without "Connection: close" and
  2102  			// they might think they can send another
  2103  			// request, but such is life with HTTP/1.1.
  2104  			return
  2105  		}
  2106  
  2107  		if d := c.server.idleTimeout(); d > 0 {
  2108  			c.rwc.SetReadDeadline(time.Now().Add(d))
  2109  		} else {
  2110  			c.rwc.SetReadDeadline(time.Time{})
  2111  		}
  2112  
  2113  		// Wait for the connection to become readable again before trying to
  2114  		// read the next request. This prevents a ReadHeaderTimeout or
  2115  		// ReadTimeout from starting until the first bytes of the next request
  2116  		// have been received.
  2117  		if _, err := c.bufr.Peek(4); err != nil {
  2118  			return
  2119  		}
  2120  
  2121  		c.rwc.SetReadDeadline(time.Time{})
  2122  	}
  2123  }
  2124  
  2125  // unencryptedHTTP2Request is an HTTP handler that initializes
  2126  // certain uninitialized fields in its *Request.
  2127  //
  2128  // It's the unencrypted version of initALPNRequest.
  2129  type unencryptedHTTP2Request struct {
  2130  	ctx context.Context
  2131  	c   net.Conn
  2132  	h   serverHandler
  2133  }
  2134  
  2135  func (h unencryptedHTTP2Request) BaseContext() context.Context { return h.ctx }
  2136  
  2137  func (h unencryptedHTTP2Request) ServeHTTP(rw ResponseWriter, req *Request) {
  2138  	if req.Body == nil {
  2139  		req.Body = NoBody
  2140  	}
  2141  	if req.RemoteAddr == "" {
  2142  		req.RemoteAddr = h.c.RemoteAddr().String()
  2143  	}
  2144  	h.h.ServeHTTP(rw, req)
  2145  }
  2146  
  2147  // unencryptedNetConnInTLSConn is used to pass an unencrypted net.Conn to
  2148  // functions that only accept a *tls.Conn.
  2149  type unencryptedNetConnInTLSConn struct {
  2150  	net.Conn // panic on all net.Conn methods
  2151  	conn     net.Conn
  2152  }
  2153  
  2154  func (c unencryptedNetConnInTLSConn) UnencryptedNetConn() net.Conn {
  2155  	return c.conn
  2156  }
  2157  
  2158  func unencryptedTLSConn(c net.Conn) *tls.Conn {
  2159  	return tls.Client(unencryptedNetConnInTLSConn{conn: c}, nil)
  2160  }
  2161  
  2162  // TLSNextProto key to use for unencrypted HTTP/2 connections.
  2163  // Not actually a TLS-negotiated protocol.
  2164  const nextProtoUnencryptedHTTP2 = "unencrypted_http2"
  2165  
  2166  func (c *conn) maybeServeUnencryptedHTTP2(ctx context.Context) bool {
  2167  	fn, ok := c.server.TLSNextProto[nextProtoUnencryptedHTTP2]
  2168  	if !ok {
  2169  		return false
  2170  	}
  2171  	hasPreface := func(c *conn, preface []byte) bool {
  2172  		c.r.setReadLimit(int64(len(preface)) - int64(c.bufr.Buffered()))
  2173  		got, err := c.bufr.Peek(len(preface))
  2174  		c.r.setInfiniteReadLimit()
  2175  		return err == nil && bytes.Equal(got, preface)
  2176  	}
  2177  	if !hasPreface(c, []byte("PRI * HTTP/2.0")) {
  2178  		return false
  2179  	}
  2180  	if !hasPreface(c, []byte("PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n")) {
  2181  		return false
  2182  	}
  2183  	c.setState(c.rwc, StateActive, skipHooks)
  2184  	h := unencryptedHTTP2Request{ctx, c.rwc, serverHandler{c.server}}
  2185  	fn(c.server, unencryptedTLSConn(c.rwc), h)
  2186  	return true
  2187  }
  2188  
  2189  func (w *response) sendExpectationFailed() {
  2190  	// TODO(bradfitz): let ServeHTTP handlers handle
  2191  	// requests with non-standard expectation[s]? Seems
  2192  	// theoretical at best, and doesn't fit into the
  2193  	// current ServeHTTP model anyway. We'd need to
  2194  	// make the ResponseWriter an optional
  2195  	// "ExpectReplier" interface or something.
  2196  	//
  2197  	// For now we'll just obey RFC 7231 5.1.1 which says
  2198  	// "A server that receives an Expect field-value other
  2199  	// than 100-continue MAY respond with a 417 (Expectation
  2200  	// Failed) status code to indicate that the unexpected
  2201  	// expectation cannot be met."
  2202  	w.Header().Set("Connection", "close")
  2203  	w.WriteHeader(StatusExpectationFailed)
  2204  	w.finishRequest()
  2205  }
  2206  
  2207  // Hijack implements the [Hijacker.Hijack] method. Our response is both a [ResponseWriter]
  2208  // and a [Hijacker].
  2209  func (w *response) Hijack() (rwc net.Conn, buf *bufio.ReadWriter, err error) {
  2210  	if w.handlerDone.Load() {
  2211  		panic("net/http: Hijack called after ServeHTTP finished")
  2212  	}
  2213  	w.disableWriteContinue()
  2214  	if w.wroteHeader {
  2215  		w.cw.flush()
  2216  	}
  2217  
  2218  	c := w.conn
  2219  	c.mu.Lock()
  2220  	defer c.mu.Unlock()
  2221  
  2222  	// Release the bufioWriter that writes to the chunk writer, it is not
  2223  	// used after a connection has been hijacked.
  2224  	rwc, buf, err = c.hijackLocked()
  2225  	if err == nil {
  2226  		putBufioWriter(w.w)
  2227  		w.w = nil
  2228  	}
  2229  	return rwc, buf, err
  2230  }
  2231  
  2232  func (w *response) CloseNotify() <-chan bool {
  2233  	w.lazyCloseNotifyMu.Lock()
  2234  	defer w.lazyCloseNotifyMu.Unlock()
  2235  	if w.handlerDone.Load() {
  2236  		panic("net/http: CloseNotify called after ServeHTTP finished")
  2237  	}
  2238  	if w.closeNotifyCh == nil {
  2239  		w.closeNotifyCh = make(chan bool, 1)
  2240  		if w.closeNotifyTriggered {
  2241  			w.closeNotifyCh <- true // action prior closeNotify call
  2242  		}
  2243  	}
  2244  	return w.closeNotifyCh
  2245  }
  2246  
  2247  func (w *response) closeNotify() {
  2248  	w.lazyCloseNotifyMu.Lock()
  2249  	defer w.lazyCloseNotifyMu.Unlock()
  2250  	if w.closeNotifyTriggered {
  2251  		return // already triggered
  2252  	}
  2253  	w.closeNotifyTriggered = true
  2254  	if w.closeNotifyCh != nil {
  2255  		w.closeNotifyCh <- true
  2256  	}
  2257  }
  2258  
  2259  func registerOnHitEOF(rc io.ReadCloser, fn func()) {
  2260  	switch v := rc.(type) {
  2261  	case *expectContinueReader:
  2262  		registerOnHitEOF(v.readCloser, fn)
  2263  	case *body:
  2264  		v.registerOnHitEOF(fn)
  2265  	default:
  2266  		panic("unexpected type " + fmt.Sprintf("%T", rc))
  2267  	}
  2268  }
  2269  
  2270  // requestBodyRemains reports whether future calls to Read
  2271  // on rc might yield more data.
  2272  func requestBodyRemains(rc io.ReadCloser) bool {
  2273  	if rc == NoBody {
  2274  		return false
  2275  	}
  2276  	switch v := rc.(type) {
  2277  	case *expectContinueReader:
  2278  		return requestBodyRemains(v.readCloser)
  2279  	case *body:
  2280  		return v.bodyRemains()
  2281  	default:
  2282  		panic("unexpected type " + fmt.Sprintf("%T", rc))
  2283  	}
  2284  }
  2285  
  2286  // The HandlerFunc type is an adapter to allow the use of
  2287  // ordinary functions as HTTP handlers. If f is a function
  2288  // with the appropriate signature, HandlerFunc(f) is a
  2289  // [Handler] that calls f.
  2290  type HandlerFunc func(ResponseWriter, *Request)
  2291  
  2292  // ServeHTTP calls f(w, r).
  2293  func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
  2294  	f(w, r)
  2295  }
  2296  
  2297  // Helper handlers
  2298  
  2299  // Error replies to the request with the specified error message and HTTP code.
  2300  // It does not otherwise end the request; the caller should ensure no further
  2301  // writes are done to w.
  2302  // The error message should be plain text.
  2303  //
  2304  // Error deletes the Content-Length header,
  2305  // sets Content-Type to “text/plain; charset=utf-8”,
  2306  // and sets X-Content-Type-Options to “nosniff”.
  2307  // This configures the header properly for the error message,
  2308  // in case the caller had set it up expecting a successful output.
  2309  func Error(w ResponseWriter, error string, code int) {
  2310  	h := w.Header()
  2311  
  2312  	// Delete the Content-Length header, which might be for some other content.
  2313  	// Assuming the error string fits in the writer's buffer, we'll figure
  2314  	// out the correct Content-Length for it later.
  2315  	//
  2316  	// We don't delete Content-Encoding, because some middleware sets
  2317  	// Content-Encoding: gzip and wraps the ResponseWriter to compress on-the-fly.
  2318  	// See https://go.dev/issue/66343.
  2319  	h.Del("Content-Length")
  2320  
  2321  	// There might be content type already set, but we reset it to
  2322  	// text/plain for the error message.
  2323  	h.Set("Content-Type", "text/plain; charset=utf-8")
  2324  	h.Set("X-Content-Type-Options", "nosniff")
  2325  	w.WriteHeader(code)
  2326  	fmt.Fprintln(w, error)
  2327  }
  2328  
  2329  // NotFound replies to the request with an HTTP 404 not found error.
  2330  func NotFound(w ResponseWriter, r *Request) { Error(w, "404 page not found", StatusNotFound) }
  2331  
  2332  // NotFoundHandler returns a simple request handler
  2333  // that replies to each request with a “404 page not found” reply.
  2334  func NotFoundHandler() Handler { return HandlerFunc(NotFound) }
  2335  
  2336  // StripPrefix returns a handler that serves HTTP requests by removing the
  2337  // given prefix from the request URL's Path (and RawPath if set) and invoking
  2338  // the handler h. StripPrefix handles a request for a path that doesn't begin
  2339  // with prefix by replying with an HTTP 404 not found error. The prefix must
  2340  // match exactly: if the prefix in the request contains escaped characters
  2341  // the reply is also an HTTP 404 not found error.
  2342  func StripPrefix(prefix string, h Handler) Handler {
  2343  	if prefix == "" {
  2344  		return h
  2345  	}
  2346  	return HandlerFunc(func(w ResponseWriter, r *Request) {
  2347  		p := strings.TrimPrefix(r.URL.Path, prefix)
  2348  		rp := strings.TrimPrefix(r.URL.RawPath, prefix)
  2349  		if len(p) < len(r.URL.Path) && (r.URL.RawPath == "" || len(rp) < len(r.URL.RawPath)) {
  2350  			r2 := new(Request)
  2351  			*r2 = *r
  2352  			r2.URL = new(url.URL)
  2353  			*r2.URL = *r.URL
  2354  			r2.URL.Path = p
  2355  			r2.URL.RawPath = rp
  2356  			h.ServeHTTP(w, r2)
  2357  		} else {
  2358  			NotFound(w, r)
  2359  		}
  2360  	})
  2361  }
  2362  
  2363  // Redirect replies to the request with a redirect to url,
  2364  // which may be a path relative to the request path.
  2365  // Any non-ASCII characters in url will be percent-encoded,
  2366  // but existing percent encodings will not be changed.
  2367  //
  2368  // The provided code should be in the 3xx range and is usually
  2369  // [StatusMovedPermanently], [StatusFound] or [StatusSeeOther].
  2370  //
  2371  // If the Content-Type header has not been set, [Redirect] sets it
  2372  // to "text/html; charset=utf-8" and writes a small HTML body.
  2373  // Setting the Content-Type header to any value, including nil,
  2374  // disables that behavior.
  2375  func Redirect(w ResponseWriter, r *Request, url string, code int) {
  2376  	if u, err := urlpkg.Parse(url); err == nil {
  2377  		// If url was relative, make its path absolute by
  2378  		// combining with request path.
  2379  		// The client would probably do this for us,
  2380  		// but doing it ourselves is more reliable.
  2381  		// See RFC 7231, section 7.1.2
  2382  		if u.Scheme == "" && u.Host == "" {
  2383  			oldpath := r.URL.Path
  2384  			if oldpath == "" { // should not happen, but avoid a crash if it does
  2385  				oldpath = "/"
  2386  			}
  2387  
  2388  			// no leading http://server
  2389  			if url == "" || url[0] != '/' {
  2390  				// make relative path absolute
  2391  				olddir, _ := path.Split(oldpath)
  2392  				url = olddir + url
  2393  			}
  2394  
  2395  			var query string
  2396  			if i := strings.Index(url, "?"); i != -1 {
  2397  				url, query = url[:i], url[i:]
  2398  			}
  2399  
  2400  			// clean up but preserve trailing slash
  2401  			trailing := strings.HasSuffix(url, "/")
  2402  			url = path.Clean(url)
  2403  			if trailing && !strings.HasSuffix(url, "/") {
  2404  				url += "/"
  2405  			}
  2406  			url += query
  2407  		}
  2408  	}
  2409  
  2410  	h := w.Header()
  2411  
  2412  	// RFC 7231 notes that a short HTML body is usually included in
  2413  	// the response because older user agents may not understand 301/307.
  2414  	// Do it only if the request didn't already have a Content-Type header.
  2415  	_, hadCT := h["Content-Type"]
  2416  
  2417  	h.Set("Location", hexEscapeNonASCII(url))
  2418  	if !hadCT && (r.Method == "GET" || r.Method == "HEAD") {
  2419  		h.Set("Content-Type", "text/html; charset=utf-8")
  2420  	}
  2421  	w.WriteHeader(code)
  2422  
  2423  	// Shouldn't send the body for POST or HEAD; that leaves GET.
  2424  	if !hadCT && r.Method == "GET" {
  2425  		body := "<a href=\"" + htmlEscape(url) + "\">" + StatusText(code) + "</a>.\n"
  2426  		fmt.Fprintln(w, body)
  2427  	}
  2428  }
  2429  
  2430  var htmlReplacer = strings.NewReplacer(
  2431  	"&", "&amp;",
  2432  	"<", "&lt;",
  2433  	">", "&gt;",
  2434  	// "&#34;" is shorter than "&quot;".
  2435  	`"`, "&#34;",
  2436  	// "&#39;" is shorter than "&apos;" and apos was not in HTML until HTML5.
  2437  	"'", "&#39;",
  2438  )
  2439  
  2440  func htmlEscape(s string) string {
  2441  	return htmlReplacer.Replace(s)
  2442  }
  2443  
  2444  // Redirect to a fixed URL
  2445  type redirectHandler struct {
  2446  	url  string
  2447  	code int
  2448  }
  2449  
  2450  func (rh *redirectHandler) ServeHTTP(w ResponseWriter, r *Request) {
  2451  	Redirect(w, r, rh.url, rh.code)
  2452  }
  2453  
  2454  // RedirectHandler returns a request handler that redirects
  2455  // each request it receives to the given url using the given
  2456  // status code.
  2457  //
  2458  // The provided code should be in the 3xx range and is usually
  2459  // [StatusMovedPermanently], [StatusFound] or [StatusSeeOther].
  2460  func RedirectHandler(url string, code int) Handler {
  2461  	return &redirectHandler{url, code}
  2462  }
  2463  
  2464  // ServeMux is an HTTP request multiplexer.
  2465  // It matches the URL of each incoming request against a list of registered
  2466  // patterns and calls the handler for the pattern that
  2467  // most closely matches the URL.
  2468  //
  2469  // # Patterns
  2470  //
  2471  // Patterns can match the method, host and path of a request.
  2472  // Some examples:
  2473  //
  2474  //   - "/index.html" matches the path "/index.html" for any host and method.
  2475  //   - "GET /static/" matches a GET request whose path begins with "/static/".
  2476  //   - "example.com/" matches any request to the host "example.com".
  2477  //   - "example.com/{$}" matches requests with host "example.com" and path "/".
  2478  //   - "/b/{bucket}/o/{objectname...}" matches paths whose first segment is "b"
  2479  //     and whose third segment is "o". The name "bucket" denotes the second
  2480  //     segment and "objectname" denotes the remainder of the path.
  2481  //
  2482  // In general, a pattern looks like
  2483  //
  2484  //	[METHOD ][HOST]/[PATH]
  2485  //
  2486  // All three parts are optional; "/" is a valid pattern.
  2487  // If METHOD is present, it must be followed by at least one space or tab.
  2488  //
  2489  // Literal (that is, non-wildcard) parts of a pattern match
  2490  // the corresponding parts of a request case-sensitively.
  2491  //
  2492  // A pattern with no method matches every method. A pattern
  2493  // with the method GET matches both GET and HEAD requests.
  2494  // Otherwise, the method must match exactly.
  2495  //
  2496  // A pattern with no host matches every host.
  2497  // A pattern with a host matches URLs on that host only.
  2498  //
  2499  // A path can include wildcard segments of the form {NAME} or {NAME...}.
  2500  // For example, "/b/{bucket}/o/{objectname...}".
  2501  // The wildcard name must be a valid Go identifier.
  2502  // Wildcards must be full path segments: they must be preceded by a slash and followed by
  2503  // either a slash or the end of the string.
  2504  // For example, "/b_{bucket}" is not a valid pattern.
  2505  //
  2506  // Normally a wildcard matches only a single path segment,
  2507  // ending at the next literal slash (not %2F) in the request URL.
  2508  // But if the "..." is present, then the wildcard matches the remainder of the URL path, including slashes.
  2509  // (Therefore it is invalid for a "..." wildcard to appear anywhere but at the end of a pattern.)
  2510  // The match for a wildcard can be obtained by calling [Request.PathValue] with the wildcard's name.
  2511  // A trailing slash in a path acts as an anonymous "..." wildcard.
  2512  //
  2513  // The special wildcard {$} matches only the end of the URL.
  2514  // For example, the pattern "/{$}" matches only the path "/",
  2515  // whereas the pattern "/" matches every path.
  2516  //
  2517  // For matching, both pattern paths and incoming request paths are unescaped segment by segment.
  2518  // So, for example, the path "/a%2Fb/100%25" is treated as having two segments, "a/b" and "100%".
  2519  // The pattern "/a%2fb/" matches it, but the pattern "/a/b/" does not.
  2520  //
  2521  // # Precedence
  2522  //
  2523  // If two or more patterns match a request, then the most specific pattern takes precedence.
  2524  // A pattern P1 is more specific than P2 if P1 matches a strict subset of P2’s requests;
  2525  // that is, if P2 matches all the requests of P1 and more.
  2526  // If neither is more specific, then the patterns conflict.
  2527  // There is one exception to this rule, for backwards compatibility:
  2528  // if two patterns would otherwise conflict and one has a host while the other does not,
  2529  // then the pattern with the host takes precedence.
  2530  // If a pattern passed to [ServeMux.Handle] or [ServeMux.HandleFunc] conflicts with
  2531  // another pattern that is already registered, those functions panic.
  2532  //
  2533  // As an example of the general rule, "/images/thumbnails/" is more specific than "/images/",
  2534  // so both can be registered.
  2535  // The former matches paths beginning with "/images/thumbnails/"
  2536  // and the latter will match any other path in the "/images/" subtree.
  2537  //
  2538  // As another example, consider the patterns "GET /" and "/index.html":
  2539  // both match a GET request for "/index.html", but the former pattern
  2540  // matches all other GET and HEAD requests, while the latter matches any
  2541  // request for "/index.html" that uses a different method.
  2542  // The patterns conflict.
  2543  //
  2544  // # Trailing-slash redirection
  2545  //
  2546  // Consider a [ServeMux] with a handler for a subtree, registered using a trailing slash or "..." wildcard.
  2547  // If the ServeMux receives a request for the subtree root without a trailing slash,
  2548  // it redirects the request by adding the trailing slash.
  2549  // This behavior can be overridden with a separate registration for the path without
  2550  // the trailing slash or "..." wildcard. For example, registering "/images/" causes ServeMux
  2551  // to redirect a request for "/images" to "/images/", unless "/images" has
  2552  // been registered separately.
  2553  //
  2554  // # Request sanitizing
  2555  //
  2556  // ServeMux also takes care of sanitizing the URL request path and the Host
  2557  // header, stripping the port number and redirecting any request containing . or
  2558  // .. segments or repeated slashes to an equivalent, cleaner URL.
  2559  // Escaped path elements such as "%2e" for "." and "%2f" for "/" are preserved
  2560  // and aren't considered separators for request routing.
  2561  //
  2562  // # Compatibility
  2563  //
  2564  // The pattern syntax and matching behavior of ServeMux changed significantly
  2565  // in Go 1.22. To restore the old behavior, set the GODEBUG environment variable
  2566  // to "httpmuxgo121=1". This setting is read once, at program startup; changes
  2567  // during execution will be ignored.
  2568  //
  2569  // The backwards-incompatible changes include:
  2570  //   - Wildcards are just ordinary literal path segments in 1.21.
  2571  //     For example, the pattern "/{x}" will match only that path in 1.21,
  2572  //     but will match any one-segment path in 1.22.
  2573  //   - In 1.21, no pattern was rejected, unless it was empty or conflicted with an existing pattern.
  2574  //     In 1.22, syntactically invalid patterns will cause [ServeMux.Handle] and [ServeMux.HandleFunc] to panic.
  2575  //     For example, in 1.21, the patterns "/{"  and "/a{x}" match themselves,
  2576  //     but in 1.22 they are invalid and will cause a panic when registered.
  2577  //   - In 1.22, each segment of a pattern is unescaped; this was not done in 1.21.
  2578  //     For example, in 1.22 the pattern "/%61" matches the path "/a" ("%61" being the URL escape sequence for "a"),
  2579  //     but in 1.21 it would match only the path "/%2561" (where "%25" is the escape for the percent sign).
  2580  //   - When matching patterns to paths, in 1.22 each segment of the path is unescaped; in 1.21, the entire path is unescaped.
  2581  //     This change mostly affects how paths with %2F escapes adjacent to slashes are treated.
  2582  //     See https://go.dev/issue/21955 for details.
  2583  type ServeMux struct {
  2584  	mu     sync.RWMutex
  2585  	tree   routingNode
  2586  	index  routingIndex
  2587  	mux121 serveMux121 // used only when GODEBUG=httpmuxgo121=1
  2588  }
  2589  
  2590  // NewServeMux allocates and returns a new [ServeMux].
  2591  func NewServeMux() *ServeMux {
  2592  	return &ServeMux{}
  2593  }
  2594  
  2595  // DefaultServeMux is the default [ServeMux] used by [Serve].
  2596  var DefaultServeMux = &defaultServeMux
  2597  
  2598  var defaultServeMux ServeMux
  2599  
  2600  // cleanPath returns the canonical path for p, eliminating . and .. elements.
  2601  func cleanPath(p string) string {
  2602  	if p == "" {
  2603  		return "/"
  2604  	}
  2605  	if p[0] != '/' {
  2606  		p = "/" + p
  2607  	}
  2608  	np := path.Clean(p)
  2609  	// path.Clean removes trailing slash except for root;
  2610  	// put the trailing slash back if necessary.
  2611  	if p[len(p)-1] == '/' && np != "/" {
  2612  		// Fast path for common case of p being the string we want:
  2613  		if len(p) == len(np)+1 && strings.HasPrefix(p, np) {
  2614  			np = p
  2615  		} else {
  2616  			np += "/"
  2617  		}
  2618  	}
  2619  	return np
  2620  }
  2621  
  2622  // stripHostPort returns h without any trailing ":<port>".
  2623  func stripHostPort(h string) string {
  2624  	// If no port on host, return unchanged
  2625  	if !strings.Contains(h, ":") {
  2626  		return h
  2627  	}
  2628  	host, _, err := net.SplitHostPort(h)
  2629  	if err != nil {
  2630  		return h // on error, return unchanged
  2631  	}
  2632  	return host
  2633  }
  2634  
  2635  // Handler returns the handler to use for the given request,
  2636  // consulting r.Method, r.Host, and r.URL.Path. It always returns
  2637  // a non-nil handler. If the path is not in its canonical form, the
  2638  // handler will be an internally-generated handler that redirects
  2639  // to the canonical path. If the host contains a port, it is ignored
  2640  // when matching handlers.
  2641  //
  2642  // The path and host are used unchanged for CONNECT requests.
  2643  //
  2644  // Handler also returns the registered pattern that matches the
  2645  // request or, in the case of internally-generated redirects,
  2646  // the path that will match after following the redirect.
  2647  //
  2648  // If there is no registered handler that applies to the request,
  2649  // Handler returns a “page not found” handler and an empty pattern.
  2650  func (mux *ServeMux) Handler(r *Request) (h Handler, pattern string) {
  2651  	if use121 {
  2652  		return mux.mux121.findHandler(r)
  2653  	}
  2654  	h, p, _, _ := mux.findHandler(r)
  2655  	return h, p
  2656  }
  2657  
  2658  // findHandler finds a handler for a request.
  2659  // If there is a matching handler, it returns it and the pattern that matched.
  2660  // Otherwise it returns a Redirect or NotFound handler with the path that would match
  2661  // after the redirect.
  2662  func (mux *ServeMux) findHandler(r *Request) (h Handler, patStr string, _ *pattern, matches []string) {
  2663  	var n *routingNode
  2664  	host := r.URL.Host
  2665  	escapedPath := r.URL.EscapedPath()
  2666  	path := escapedPath
  2667  	// CONNECT requests are not canonicalized.
  2668  	if r.Method == "CONNECT" {
  2669  		// If r.URL.Path is /tree and its handler is not registered,
  2670  		// the /tree -> /tree/ redirect applies to CONNECT requests
  2671  		// but the path canonicalization does not.
  2672  		_, _, u := mux.matchOrRedirect(host, r.Method, path, r.URL)
  2673  		if u != nil {
  2674  			return RedirectHandler(u.String(), StatusMovedPermanently), u.Path, nil, nil
  2675  		}
  2676  		// Redo the match, this time with r.Host instead of r.URL.Host.
  2677  		// Pass a nil URL to skip the trailing-slash redirect logic.
  2678  		n, matches, _ = mux.matchOrRedirect(r.Host, r.Method, path, nil)
  2679  	} else {
  2680  		// All other requests have any port stripped and path cleaned
  2681  		// before passing to mux.handler.
  2682  		host = stripHostPort(r.Host)
  2683  		path = cleanPath(path)
  2684  
  2685  		// If the given path is /tree and its handler is not registered,
  2686  		// redirect for /tree/.
  2687  		var u *url.URL
  2688  		n, matches, u = mux.matchOrRedirect(host, r.Method, path, r.URL)
  2689  		if u != nil {
  2690  			return RedirectHandler(u.String(), StatusMovedPermanently), u.Path, nil, nil
  2691  		}
  2692  		if path != escapedPath {
  2693  			// Redirect to cleaned path.
  2694  			patStr := ""
  2695  			if n != nil {
  2696  				patStr = n.pattern.String()
  2697  			}
  2698  			u := &url.URL{Path: path, RawQuery: r.URL.RawQuery}
  2699  			return RedirectHandler(u.String(), StatusMovedPermanently), patStr, nil, nil
  2700  		}
  2701  	}
  2702  	if n == nil {
  2703  		// We didn't find a match with the request method. To distinguish between
  2704  		// Not Found and Method Not Allowed, see if there is another pattern that
  2705  		// matches except for the method.
  2706  		allowedMethods := mux.matchingMethods(host, path)
  2707  		if len(allowedMethods) > 0 {
  2708  			return HandlerFunc(func(w ResponseWriter, r *Request) {
  2709  				w.Header().Set("Allow", strings.Join(allowedMethods, ", "))
  2710  				Error(w, StatusText(StatusMethodNotAllowed), StatusMethodNotAllowed)
  2711  			}), "", nil, nil
  2712  		}
  2713  		return NotFoundHandler(), "", nil, nil
  2714  	}
  2715  	return n.handler, n.pattern.String(), n.pattern, matches
  2716  }
  2717  
  2718  // matchOrRedirect looks up a node in the tree that matches the host, method and path.
  2719  //
  2720  // If the url argument is non-nil, handler also deals with trailing-slash
  2721  // redirection: when a path doesn't match exactly, the match is tried again
  2722  // after appending "/" to the path. If that second match succeeds, the last
  2723  // return value is the URL to redirect to.
  2724  func (mux *ServeMux) matchOrRedirect(host, method, path string, u *url.URL) (_ *routingNode, matches []string, redirectTo *url.URL) {
  2725  	mux.mu.RLock()
  2726  	defer mux.mu.RUnlock()
  2727  
  2728  	n, matches := mux.tree.match(host, method, path)
  2729  	// If we have an exact match, or we were asked not to try trailing-slash redirection,
  2730  	// or the URL already has a trailing slash, then we're done.
  2731  	if !exactMatch(n, path) && u != nil && !strings.HasSuffix(path, "/") {
  2732  		// If there is an exact match with a trailing slash, then redirect.
  2733  		path += "/"
  2734  		n2, _ := mux.tree.match(host, method, path)
  2735  		if exactMatch(n2, path) {
  2736  			return nil, nil, &url.URL{Path: cleanPath(u.Path) + "/", RawQuery: u.RawQuery}
  2737  		}
  2738  	}
  2739  	return n, matches, nil
  2740  }
  2741  
  2742  // exactMatch reports whether the node's pattern exactly matches the path.
  2743  // As a special case, if the node is nil, exactMatch return false.
  2744  //
  2745  // Before wildcards were introduced, it was clear that an exact match meant
  2746  // that the pattern and path were the same string. The only other possibility
  2747  // was that a trailing-slash pattern, like "/", matched a path longer than
  2748  // it, like "/a".
  2749  //
  2750  // With wildcards, we define an inexact match as any one where a multi wildcard
  2751  // matches a non-empty string. All other matches are exact.
  2752  // For example, these are all exact matches:
  2753  //
  2754  //	pattern   path
  2755  //	/a        /a
  2756  //	/{x}      /a
  2757  //	/a/{$}    /a/
  2758  //	/a/       /a/
  2759  //
  2760  // The last case has a multi wildcard (implicitly), but the match is exact because
  2761  // the wildcard matches the empty string.
  2762  //
  2763  // Examples of matches that are not exact:
  2764  //
  2765  //	pattern   path
  2766  //	/         /a
  2767  //	/a/{x...} /a/b
  2768  func exactMatch(n *routingNode, path string) bool {
  2769  	if n == nil {
  2770  		return false
  2771  	}
  2772  	// We can't directly implement the definition (empty match for multi
  2773  	// wildcard) because we don't record a match for anonymous multis.
  2774  
  2775  	// If there is no multi, the match is exact.
  2776  	if !n.pattern.lastSegment().multi {
  2777  		return true
  2778  	}
  2779  
  2780  	// If the path doesn't end in a trailing slash, then the multi match
  2781  	// is non-empty.
  2782  	if len(path) > 0 && path[len(path)-1] != '/' {
  2783  		return false
  2784  	}
  2785  	// Only patterns ending in {$} or a multi wildcard can
  2786  	// match a path with a trailing slash.
  2787  	// For the match to be exact, the number of pattern
  2788  	// segments should be the same as the number of slashes in the path.
  2789  	// E.g. "/a/b/{$}" and "/a/b/{...}" exactly match "/a/b/", but "/a/" does not.
  2790  	return len(n.pattern.segments) == strings.Count(path, "/")
  2791  }
  2792  
  2793  // matchingMethods return a sorted list of all methods that would match with the given host and path.
  2794  func (mux *ServeMux) matchingMethods(host, path string) []string {
  2795  	// Hold the read lock for the entire method so that the two matches are done
  2796  	// on the same set of registered patterns.
  2797  	mux.mu.RLock()
  2798  	defer mux.mu.RUnlock()
  2799  	ms := map[string]bool{}
  2800  	mux.tree.matchingMethods(host, path, ms)
  2801  	// matchOrRedirect will try appending a trailing slash if there is no match.
  2802  	if !strings.HasSuffix(path, "/") {
  2803  		mux.tree.matchingMethods(host, path+"/", ms)
  2804  	}
  2805  	return slices.Sorted(maps.Keys(ms))
  2806  }
  2807  
  2808  // ServeHTTP dispatches the request to the handler whose
  2809  // pattern most closely matches the request URL.
  2810  func (mux *ServeMux) ServeHTTP(w ResponseWriter, r *Request) {
  2811  	if r.RequestURI == "*" {
  2812  		if r.ProtoAtLeast(1, 1) {
  2813  			w.Header().Set("Connection", "close")
  2814  		}
  2815  		w.WriteHeader(StatusBadRequest)
  2816  		return
  2817  	}
  2818  	var h Handler
  2819  	if use121 {
  2820  		h, _ = mux.mux121.findHandler(r)
  2821  	} else {
  2822  		h, r.Pattern, r.pat, r.matches = mux.findHandler(r)
  2823  	}
  2824  	h.ServeHTTP(w, r)
  2825  }
  2826  
  2827  // The four functions below all call ServeMux.register so that callerLocation
  2828  // always refers to user code.
  2829  
  2830  // Handle registers the handler for the given pattern.
  2831  // If the given pattern conflicts, with one that is already registered, Handle
  2832  // panics.
  2833  func (mux *ServeMux) Handle(pattern string, handler Handler) {
  2834  	if use121 {
  2835  		mux.mux121.handle(pattern, handler)
  2836  	} else {
  2837  		mux.register(pattern, handler)
  2838  	}
  2839  }
  2840  
  2841  // HandleFunc registers the handler function for the given pattern.
  2842  // If the given pattern conflicts, with one that is already registered, HandleFunc
  2843  // panics.
  2844  func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
  2845  	if use121 {
  2846  		mux.mux121.handleFunc(pattern, handler)
  2847  	} else {
  2848  		mux.register(pattern, HandlerFunc(handler))
  2849  	}
  2850  }
  2851  
  2852  // Handle registers the handler for the given pattern in [DefaultServeMux].
  2853  // The documentation for [ServeMux] explains how patterns are matched.
  2854  func Handle(pattern string, handler Handler) {
  2855  	if use121 {
  2856  		DefaultServeMux.mux121.handle(pattern, handler)
  2857  	} else {
  2858  		DefaultServeMux.register(pattern, handler)
  2859  	}
  2860  }
  2861  
  2862  // HandleFunc registers the handler function for the given pattern in [DefaultServeMux].
  2863  // The documentation for [ServeMux] explains how patterns are matched.
  2864  func HandleFunc(pattern string, handler func(ResponseWriter, *Request)) {
  2865  	if use121 {
  2866  		DefaultServeMux.mux121.handleFunc(pattern, handler)
  2867  	} else {
  2868  		DefaultServeMux.register(pattern, HandlerFunc(handler))
  2869  	}
  2870  }
  2871  
  2872  func (mux *ServeMux) register(pattern string, handler Handler) {
  2873  	if err := mux.registerErr(pattern, handler); err != nil {
  2874  		panic(err)
  2875  	}
  2876  }
  2877  
  2878  func (mux *ServeMux) registerErr(patstr string, handler Handler) error {
  2879  	if patstr == "" {
  2880  		return errors.New("http: invalid pattern")
  2881  	}
  2882  	if handler == nil {
  2883  		return errors.New("http: nil handler")
  2884  	}
  2885  	if f, ok := handler.(HandlerFunc); ok && f == nil {
  2886  		return errors.New("http: nil handler")
  2887  	}
  2888  
  2889  	pat, err := parsePattern(patstr)
  2890  	if err != nil {
  2891  		return fmt.Errorf("parsing %q: %w", patstr, err)
  2892  	}
  2893  
  2894  	// Get the caller's location, for better conflict error messages.
  2895  	// Skip register and whatever calls it.
  2896  	_, file, line, ok := runtime.Caller(3)
  2897  	if !ok {
  2898  		pat.loc = "unknown location"
  2899  	} else {
  2900  		pat.loc = fmt.Sprintf("%s:%d", file, line)
  2901  	}
  2902  
  2903  	mux.mu.Lock()
  2904  	defer mux.mu.Unlock()
  2905  	// Check for conflict.
  2906  	if err := mux.index.possiblyConflictingPatterns(pat, func(pat2 *pattern) error {
  2907  		if pat.conflictsWith(pat2) {
  2908  			d := describeConflict(pat, pat2)
  2909  			return fmt.Errorf("pattern %q (registered at %s) conflicts with pattern %q (registered at %s):\n%s",
  2910  				pat, pat.loc, pat2, pat2.loc, d)
  2911  		}
  2912  		return nil
  2913  	}); err != nil {
  2914  		return err
  2915  	}
  2916  	mux.tree.addPattern(pat, handler)
  2917  	mux.index.addPattern(pat)
  2918  	return nil
  2919  }
  2920  
  2921  // Serve accepts incoming HTTP connections on the listener l,
  2922  // creating a new service goroutine for each. The service goroutines
  2923  // read requests and then call handler to reply to them.
  2924  //
  2925  // The handler is typically nil, in which case [DefaultServeMux] is used.
  2926  //
  2927  // HTTP/2 support is only enabled if the Listener returns [*tls.Conn]
  2928  // connections and they were configured with "h2" in the TLS
  2929  // Config.NextProtos.
  2930  //
  2931  // Serve always returns a non-nil error.
  2932  func Serve(l net.Listener, handler Handler) error {
  2933  	srv := &Server{Handler: handler}
  2934  	return srv.Serve(l)
  2935  }
  2936  
  2937  // ServeTLS accepts incoming HTTPS connections on the listener l,
  2938  // creating a new service goroutine for each. The service goroutines
  2939  // read requests and then call handler to reply to them.
  2940  //
  2941  // The handler is typically nil, in which case [DefaultServeMux] is used.
  2942  //
  2943  // Additionally, files containing a certificate and matching private key
  2944  // for the server must be provided. If the certificate is signed by a
  2945  // certificate authority, the certFile should be the concatenation
  2946  // of the server's certificate, any intermediates, and the CA's certificate.
  2947  //
  2948  // ServeTLS always returns a non-nil error.
  2949  func ServeTLS(l net.Listener, handler Handler, certFile, keyFile string) error {
  2950  	srv := &Server{Handler: handler}
  2951  	return srv.ServeTLS(l, certFile, keyFile)
  2952  }
  2953  
  2954  // A Server defines parameters for running an HTTP server.
  2955  // The zero value for Server is a valid configuration.
  2956  type Server struct {
  2957  	// Addr optionally specifies the TCP address for the server to listen on,
  2958  	// in the form "host:port". If empty, ":http" (port 80) is used.
  2959  	// The service names are defined in RFC 6335 and assigned by IANA.
  2960  	// See net.Dial for details of the address format.
  2961  	Addr string
  2962  
  2963  	Handler Handler // handler to invoke, http.DefaultServeMux if nil
  2964  
  2965  	// DisableGeneralOptionsHandler, if true, passes "OPTIONS *" requests to the Handler,
  2966  	// otherwise responds with 200 OK and Content-Length: 0.
  2967  	DisableGeneralOptionsHandler bool
  2968  
  2969  	// TLSConfig optionally provides a TLS configuration for use
  2970  	// by ServeTLS and ListenAndServeTLS. Note that this value is
  2971  	// cloned by ServeTLS and ListenAndServeTLS, so it's not
  2972  	// possible to modify the configuration with methods like
  2973  	// tls.Config.SetSessionTicketKeys. To use
  2974  	// SetSessionTicketKeys, use Server.Serve with a TLS Listener
  2975  	// instead.
  2976  	TLSConfig *tls.Config
  2977  
  2978  	// ReadTimeout is the maximum duration for reading the entire
  2979  	// request, including the body. A zero or negative value means
  2980  	// there will be no timeout.
  2981  	//
  2982  	// Because ReadTimeout does not let Handlers make per-request
  2983  	// decisions on each request body's acceptable deadline or
  2984  	// upload rate, most users will prefer to use
  2985  	// ReadHeaderTimeout. It is valid to use them both.
  2986  	ReadTimeout time.Duration
  2987  
  2988  	// ReadHeaderTimeout is the amount of time allowed to read
  2989  	// request headers. The connection's read deadline is reset
  2990  	// after reading the headers and the Handler can decide what
  2991  	// is considered too slow for the body. If zero, the value of
  2992  	// ReadTimeout is used. If negative, or if zero and ReadTimeout
  2993  	// is zero or negative, there is no timeout.
  2994  	ReadHeaderTimeout time.Duration
  2995  
  2996  	// WriteTimeout is the maximum duration before timing out
  2997  	// writes of the response. It is reset whenever a new
  2998  	// request's header is read. Like ReadTimeout, it does not
  2999  	// let Handlers make decisions on a per-request basis.
  3000  	// A zero or negative value means there will be no timeout.
  3001  	WriteTimeout time.Duration
  3002  
  3003  	// IdleTimeout is the maximum amount of time to wait for the
  3004  	// next request when keep-alives are enabled. If zero, the value
  3005  	// of ReadTimeout is used. If negative, or if zero and ReadTimeout
  3006  	// is zero or negative, there is no timeout.
  3007  	IdleTimeout time.Duration
  3008  
  3009  	// MaxHeaderBytes controls the maximum number of bytes the
  3010  	// server will read parsing the request header's keys and
  3011  	// values, including the request line. It does not limit the
  3012  	// size of the request body.
  3013  	// If zero, DefaultMaxHeaderBytes is used.
  3014  	MaxHeaderBytes int
  3015  
  3016  	// TLSNextProto optionally specifies a function to take over
  3017  	// ownership of the provided TLS connection when an ALPN
  3018  	// protocol upgrade has occurred. The map key is the protocol
  3019  	// name negotiated. The Handler argument should be used to
  3020  	// handle HTTP requests and will initialize the Request's TLS
  3021  	// and RemoteAddr if not already set. The connection is
  3022  	// automatically closed when the function returns.
  3023  	// If TLSNextProto is not nil, HTTP/2 support is not enabled
  3024  	// automatically.
  3025  	TLSNextProto map[string]func(*Server, *tls.Conn, Handler)
  3026  
  3027  	// ConnState specifies an optional callback function that is
  3028  	// called when a client connection changes state. See the
  3029  	// ConnState type and associated constants for details.
  3030  	ConnState func(net.Conn, ConnState)
  3031  
  3032  	// ErrorLog specifies an optional logger for errors accepting
  3033  	// connections, unexpected behavior from handlers, and
  3034  	// underlying FileSystem errors.
  3035  	// If nil, logging is done via the log package's standard logger.
  3036  	ErrorLog *log.Logger
  3037  
  3038  	// BaseContext optionally specifies a function that returns
  3039  	// the base context for incoming requests on this server.
  3040  	// The provided Listener is the specific Listener that's
  3041  	// about to start accepting requests.
  3042  	// If BaseContext is nil, the default is context.Background().
  3043  	// If non-nil, it must return a non-nil context.
  3044  	BaseContext func(net.Listener) context.Context
  3045  
  3046  	// ConnContext optionally specifies a function that modifies
  3047  	// the context used for a new connection c. The provided ctx
  3048  	// is derived from the base context and has a ServerContextKey
  3049  	// value.
  3050  	ConnContext func(ctx context.Context, c net.Conn) context.Context
  3051  
  3052  	// HTTP2 configures HTTP/2 connections.
  3053  	//
  3054  	// This field does not yet have any effect.
  3055  	// See https://go.dev/issue/67813.
  3056  	HTTP2 *HTTP2Config
  3057  
  3058  	// Protocols is the set of protocols accepted by the server.
  3059  	//
  3060  	// If Protocols includes UnencryptedHTTP2, the server will accept
  3061  	// unencrypted HTTP/2 connections. The server can serve both
  3062  	// HTTP/1 and unencrypted HTTP/2 on the same address and port.
  3063  	//
  3064  	// If Protocols is nil, the default is usually HTTP/1 and HTTP/2.
  3065  	// If TLSNextProto is non-nil and does not contain an "h2" entry,
  3066  	// the default is HTTP/1 only.
  3067  	Protocols *Protocols
  3068  
  3069  	inShutdown atomic.Bool // true when server is in shutdown
  3070  
  3071  	disableKeepAlives atomic.Bool
  3072  	nextProtoOnce     sync.Once // guards setupHTTP2_* init
  3073  	nextProtoErr      error     // result of http2.ConfigureServer if used
  3074  
  3075  	mu         sync.Mutex
  3076  	listeners  map[*net.Listener]struct{}
  3077  	activeConn map[*conn]struct{}
  3078  	onShutdown []func()
  3079  
  3080  	listenerGroup sync.WaitGroup
  3081  }
  3082  
  3083  // Close immediately closes all active net.Listeners and any
  3084  // connections in state [StateNew], [StateActive], or [StateIdle]. For a
  3085  // graceful shutdown, use [Server.Shutdown].
  3086  //
  3087  // Close does not attempt to close (and does not even know about)
  3088  // any hijacked connections, such as WebSockets.
  3089  //
  3090  // Close returns any error returned from closing the [Server]'s
  3091  // underlying Listener(s).
  3092  func (s *Server) Close() error {
  3093  	s.inShutdown.Store(true)
  3094  	s.mu.Lock()
  3095  	defer s.mu.Unlock()
  3096  	err := s.closeListenersLocked()
  3097  
  3098  	// Unlock s.mu while waiting for listenerGroup.
  3099  	// The group Add and Done calls are made with s.mu held,
  3100  	// to avoid adding a new listener in the window between
  3101  	// us setting inShutdown above and waiting here.
  3102  	s.mu.Unlock()
  3103  	s.listenerGroup.Wait()
  3104  	s.mu.Lock()
  3105  
  3106  	for c := range s.activeConn {
  3107  		c.rwc.Close()
  3108  		delete(s.activeConn, c)
  3109  	}
  3110  	return err
  3111  }
  3112  
  3113  // shutdownPollIntervalMax is the max polling interval when checking
  3114  // quiescence during Server.Shutdown. Polling starts with a small
  3115  // interval and backs off to the max.
  3116  // Ideally we could find a solution that doesn't involve polling,
  3117  // but which also doesn't have a high runtime cost (and doesn't
  3118  // involve any contentious mutexes), but that is left as an
  3119  // exercise for the reader.
  3120  const shutdownPollIntervalMax = 500 * time.Millisecond
  3121  
  3122  // Shutdown gracefully shuts down the server without interrupting any
  3123  // active connections. Shutdown works by first closing all open
  3124  // listeners, then closing all idle connections, and then waiting
  3125  // indefinitely for connections to return to idle and then shut down.
  3126  // If the provided context expires before the shutdown is complete,
  3127  // Shutdown returns the context's error, otherwise it returns any
  3128  // error returned from closing the [Server]'s underlying Listener(s).
  3129  //
  3130  // When Shutdown is called, [Serve], [ListenAndServe], and
  3131  // [ListenAndServeTLS] immediately return [ErrServerClosed]. Make sure the
  3132  // program doesn't exit and waits instead for Shutdown to return.
  3133  //
  3134  // Shutdown does not attempt to close nor wait for hijacked
  3135  // connections such as WebSockets. The caller of Shutdown should
  3136  // separately notify such long-lived connections of shutdown and wait
  3137  // for them to close, if desired. See [Server.RegisterOnShutdown] for a way to
  3138  // register shutdown notification functions.
  3139  //
  3140  // Once Shutdown has been called on a server, it may not be reused;
  3141  // future calls to methods such as Serve will return ErrServerClosed.
  3142  func (s *Server) Shutdown(ctx context.Context) error {
  3143  	s.inShutdown.Store(true)
  3144  
  3145  	s.mu.Lock()
  3146  	lnerr := s.closeListenersLocked()
  3147  	for _, f := range s.onShutdown {
  3148  		go f()
  3149  	}
  3150  	s.mu.Unlock()
  3151  	s.listenerGroup.Wait()
  3152  
  3153  	pollIntervalBase := time.Millisecond
  3154  	nextPollInterval := func() time.Duration {
  3155  		// Add 10% jitter.
  3156  		interval := pollIntervalBase + time.Duration(rand.Intn(int(pollIntervalBase/10)))
  3157  		// Double and clamp for next time.
  3158  		pollIntervalBase *= 2
  3159  		if pollIntervalBase > shutdownPollIntervalMax {
  3160  			pollIntervalBase = shutdownPollIntervalMax
  3161  		}
  3162  		return interval
  3163  	}
  3164  
  3165  	timer := time.NewTimer(nextPollInterval())
  3166  	defer timer.Stop()
  3167  	for {
  3168  		if s.closeIdleConns() {
  3169  			return lnerr
  3170  		}
  3171  		select {
  3172  		case <-ctx.Done():
  3173  			return ctx.Err()
  3174  		case <-timer.C:
  3175  			timer.Reset(nextPollInterval())
  3176  		}
  3177  	}
  3178  }
  3179  
  3180  // RegisterOnShutdown registers a function to call on [Server.Shutdown].
  3181  // This can be used to gracefully shutdown connections that have
  3182  // undergone ALPN protocol upgrade or that have been hijacked.
  3183  // This function should start protocol-specific graceful shutdown,
  3184  // but should not wait for shutdown to complete.
  3185  func (s *Server) RegisterOnShutdown(f func()) {
  3186  	s.mu.Lock()
  3187  	s.onShutdown = append(s.onShutdown, f)
  3188  	s.mu.Unlock()
  3189  }
  3190  
  3191  // closeIdleConns closes all idle connections and reports whether the
  3192  // server is quiescent.
  3193  func (s *Server) closeIdleConns() bool {
  3194  	s.mu.Lock()
  3195  	defer s.mu.Unlock()
  3196  	quiescent := true
  3197  	for c := range s.activeConn {
  3198  		st, unixSec := c.getState()
  3199  		// Issue 22682: treat StateNew connections as if
  3200  		// they're idle if we haven't read the first request's
  3201  		// header in over 5 seconds.
  3202  		if st == StateNew && unixSec < time.Now().Unix()-5 {
  3203  			st = StateIdle
  3204  		}
  3205  		if st != StateIdle || unixSec == 0 {
  3206  			// Assume unixSec == 0 means it's a very new
  3207  			// connection, without state set yet.
  3208  			quiescent = false
  3209  			continue
  3210  		}
  3211  		c.rwc.Close()
  3212  		delete(s.activeConn, c)
  3213  	}
  3214  	return quiescent
  3215  }
  3216  
  3217  func (s *Server) closeListenersLocked() error {
  3218  	var err error
  3219  	for ln := range s.listeners {
  3220  		if cerr := (*ln).Close(); cerr != nil && err == nil {
  3221  			err = cerr
  3222  		}
  3223  	}
  3224  	return err
  3225  }
  3226  
  3227  // A ConnState represents the state of a client connection to a server.
  3228  // It's used by the optional [Server.ConnState] hook.
  3229  type ConnState int
  3230  
  3231  const (
  3232  	// StateNew represents a new connection that is expected to
  3233  	// send a request immediately. Connections begin at this
  3234  	// state and then transition to either StateActive or
  3235  	// StateClosed.
  3236  	StateNew ConnState = iota
  3237  
  3238  	// StateActive represents a connection that has read 1 or more
  3239  	// bytes of a request. The Server.ConnState hook for
  3240  	// StateActive fires before the request has entered a handler
  3241  	// and doesn't fire again until the request has been
  3242  	// handled. After the request is handled, the state
  3243  	// transitions to StateClosed, StateHijacked, or StateIdle.
  3244  	// For HTTP/2, StateActive fires on the transition from zero
  3245  	// to one active request, and only transitions away once all
  3246  	// active requests are complete. That means that ConnState
  3247  	// cannot be used to do per-request work; ConnState only notes
  3248  	// the overall state of the connection.
  3249  	StateActive
  3250  
  3251  	// StateIdle represents a connection that has finished
  3252  	// handling a request and is in the keep-alive state, waiting
  3253  	// for a new request. Connections transition from StateIdle
  3254  	// to either StateActive or StateClosed.
  3255  	StateIdle
  3256  
  3257  	// StateHijacked represents a hijacked connection.
  3258  	// This is a terminal state. It does not transition to StateClosed.
  3259  	StateHijacked
  3260  
  3261  	// StateClosed represents a closed connection.
  3262  	// This is a terminal state. Hijacked connections do not
  3263  	// transition to StateClosed.
  3264  	StateClosed
  3265  )
  3266  
  3267  var stateName = map[ConnState]string{
  3268  	StateNew:      "new",
  3269  	StateActive:   "active",
  3270  	StateIdle:     "idle",
  3271  	StateHijacked: "hijacked",
  3272  	StateClosed:   "closed",
  3273  }
  3274  
  3275  func (c ConnState) String() string {
  3276  	return stateName[c]
  3277  }
  3278  
  3279  // serverHandler delegates to either the server's Handler or
  3280  // DefaultServeMux and also handles "OPTIONS *" requests.
  3281  type serverHandler struct {
  3282  	srv *Server
  3283  }
  3284  
  3285  // ServeHTTP should be an internal detail,
  3286  // but widely used packages access it using linkname.
  3287  // Notable members of the hall of shame include:
  3288  //   - github.com/erda-project/erda-infra
  3289  //
  3290  // Do not remove or change the type signature.
  3291  // See go.dev/issue/67401.
  3292  //
  3293  //go:linkname badServeHTTP net/http.serverHandler.ServeHTTP
  3294  func (sh serverHandler) ServeHTTP(rw ResponseWriter, req *Request) {
  3295  	handler := sh.srv.Handler
  3296  	if handler == nil {
  3297  		handler = DefaultServeMux
  3298  	}
  3299  	if !sh.srv.DisableGeneralOptionsHandler && req.RequestURI == "*" && req.Method == "OPTIONS" {
  3300  		handler = globalOptionsHandler{}
  3301  	}
  3302  
  3303  	handler.ServeHTTP(rw, req)
  3304  }
  3305  
  3306  func badServeHTTP(serverHandler, ResponseWriter, *Request)
  3307  
  3308  // AllowQuerySemicolons returns a handler that serves requests by converting any
  3309  // unescaped semicolons in the URL query to ampersands, and invoking the handler h.
  3310  //
  3311  // This restores the pre-Go 1.17 behavior of splitting query parameters on both
  3312  // semicolons and ampersands. (See golang.org/issue/25192). Note that this
  3313  // behavior doesn't match that of many proxies, and the mismatch can lead to
  3314  // security issues.
  3315  //
  3316  // AllowQuerySemicolons should be invoked before [Request.ParseForm] is called.
  3317  func AllowQuerySemicolons(h Handler) Handler {
  3318  	return HandlerFunc(func(w ResponseWriter, r *Request) {
  3319  		if strings.Contains(r.URL.RawQuery, ";") {
  3320  			r2 := new(Request)
  3321  			*r2 = *r
  3322  			r2.URL = new(url.URL)
  3323  			*r2.URL = *r.URL
  3324  			r2.URL.RawQuery = strings.ReplaceAll(r.URL.RawQuery, ";", "&")
  3325  			h.ServeHTTP(w, r2)
  3326  		} else {
  3327  			h.ServeHTTP(w, r)
  3328  		}
  3329  	})
  3330  }
  3331  
  3332  // ListenAndServe listens on the TCP network address s.Addr and then
  3333  // calls [Serve] to handle requests on incoming connections.
  3334  // Accepted connections are configured to enable TCP keep-alives.
  3335  //
  3336  // If s.Addr is blank, ":http" is used.
  3337  //
  3338  // ListenAndServe always returns a non-nil error. After [Server.Shutdown] or [Server.Close],
  3339  // the returned error is [ErrServerClosed].
  3340  func (s *Server) ListenAndServe() error {
  3341  	if s.shuttingDown() {
  3342  		return ErrServerClosed
  3343  	}
  3344  	addr := s.Addr
  3345  	if addr == "" {
  3346  		addr = ":http"
  3347  	}
  3348  	ln, err := net.Listen("tcp", addr)
  3349  	if err != nil {
  3350  		return err
  3351  	}
  3352  	return s.Serve(ln)
  3353  }
  3354  
  3355  var testHookServerServe func(*Server, net.Listener) // used if non-nil
  3356  
  3357  // shouldConfigureHTTP2ForServe reports whether Server.Serve should configure
  3358  // automatic HTTP/2. (which sets up the s.TLSNextProto map)
  3359  func (s *Server) shouldConfigureHTTP2ForServe() bool {
  3360  	if s.TLSConfig == nil {
  3361  		// Compatibility with Go 1.6:
  3362  		// If there's no TLSConfig, it's possible that the user just
  3363  		// didn't set it on the http.Server, but did pass it to
  3364  		// tls.NewListener and passed that listener to Serve.
  3365  		// So we should configure HTTP/2 (to set up s.TLSNextProto)
  3366  		// in case the listener returns an "h2" *tls.Conn.
  3367  		return true
  3368  	}
  3369  	if s.protocols().UnencryptedHTTP2() {
  3370  		return true
  3371  	}
  3372  	// The user specified a TLSConfig on their http.Server.
  3373  	// In this, case, only configure HTTP/2 if their tls.Config
  3374  	// explicitly mentions "h2". Otherwise http2.ConfigureServer
  3375  	// would modify the tls.Config to add it, but they probably already
  3376  	// passed this tls.Config to tls.NewListener. And if they did,
  3377  	// it's too late anyway to fix it. It would only be potentially racy.
  3378  	// See Issue 15908.
  3379  	return slices.Contains(s.TLSConfig.NextProtos, http2NextProtoTLS)
  3380  }
  3381  
  3382  // ErrServerClosed is returned by the [Server.Serve], [ServeTLS], [ListenAndServe],
  3383  // and [ListenAndServeTLS] methods after a call to [Server.Shutdown] or [Server.Close].
  3384  var ErrServerClosed = errors.New("http: Server closed")
  3385  
  3386  // Serve accepts incoming connections on the Listener l, creating a
  3387  // new service goroutine for each. The service goroutines read requests and
  3388  // then call s.Handler to reply to them.
  3389  //
  3390  // HTTP/2 support is only enabled if the Listener returns [*tls.Conn]
  3391  // connections and they were configured with "h2" in the TLS
  3392  // Config.NextProtos.
  3393  //
  3394  // Serve always returns a non-nil error and closes l.
  3395  // After [Server.Shutdown] or [Server.Close], the returned error is [ErrServerClosed].
  3396  func (s *Server) Serve(l net.Listener) error {
  3397  	if fn := testHookServerServe; fn != nil {
  3398  		fn(s, l) // call hook with unwrapped listener
  3399  	}
  3400  
  3401  	origListener := l
  3402  	l = &onceCloseListener{Listener: l}
  3403  	defer l.Close()
  3404  
  3405  	if err := s.setupHTTP2_Serve(); err != nil {
  3406  		return err
  3407  	}
  3408  
  3409  	if !s.trackListener(&l, true) {
  3410  		return ErrServerClosed
  3411  	}
  3412  	defer s.trackListener(&l, false)
  3413  
  3414  	baseCtx := context.Background()
  3415  	if s.BaseContext != nil {
  3416  		baseCtx = s.BaseContext(origListener)
  3417  		if baseCtx == nil {
  3418  			panic("BaseContext returned a nil context")
  3419  		}
  3420  	}
  3421  
  3422  	var tempDelay time.Duration // how long to sleep on accept failure
  3423  
  3424  	ctx := context.WithValue(baseCtx, ServerContextKey, s)
  3425  	for {
  3426  		rw, err := l.Accept()
  3427  		if err != nil {
  3428  			if s.shuttingDown() {
  3429  				return ErrServerClosed
  3430  			}
  3431  			if ne, ok := err.(net.Error); ok && ne.Temporary() {
  3432  				if tempDelay == 0 {
  3433  					tempDelay = 5 * time.Millisecond
  3434  				} else {
  3435  					tempDelay *= 2
  3436  				}
  3437  				if max := 1 * time.Second; tempDelay > max {
  3438  					tempDelay = max
  3439  				}
  3440  				s.logf("http: Accept error: %v; retrying in %v", err, tempDelay)
  3441  				time.Sleep(tempDelay)
  3442  				continue
  3443  			}
  3444  			return err
  3445  		}
  3446  		connCtx := ctx
  3447  		if cc := s.ConnContext; cc != nil {
  3448  			connCtx = cc(connCtx, rw)
  3449  			if connCtx == nil {
  3450  				panic("ConnContext returned nil")
  3451  			}
  3452  		}
  3453  		tempDelay = 0
  3454  		c := s.newConn(rw)
  3455  		c.setState(c.rwc, StateNew, runHooks) // before Serve can return
  3456  		go c.serve(connCtx)
  3457  	}
  3458  }
  3459  
  3460  // ServeTLS accepts incoming connections on the Listener l, creating a
  3461  // new service goroutine for each. The service goroutines perform TLS
  3462  // setup and then read requests, calling s.Handler to reply to them.
  3463  //
  3464  // Files containing a certificate and matching private key for the
  3465  // server must be provided if neither the [Server]'s
  3466  // TLSConfig.Certificates, TLSConfig.GetCertificate nor
  3467  // config.GetConfigForClient are populated.
  3468  // If the certificate is signed by a certificate authority, the
  3469  // certFile should be the concatenation of the server's certificate,
  3470  // any intermediates, and the CA's certificate.
  3471  //
  3472  // ServeTLS always returns a non-nil error. After [Server.Shutdown] or [Server.Close], the
  3473  // returned error is [ErrServerClosed].
  3474  func (s *Server) ServeTLS(l net.Listener, certFile, keyFile string) error {
  3475  	// Setup HTTP/2 before s.Serve, to initialize s.TLSConfig
  3476  	// before we clone it and create the TLS Listener.
  3477  	if err := s.setupHTTP2_ServeTLS(); err != nil {
  3478  		return err
  3479  	}
  3480  
  3481  	config := cloneTLSConfig(s.TLSConfig)
  3482  	config.NextProtos = adjustNextProtos(config.NextProtos, s.protocols())
  3483  
  3484  	configHasCert := len(config.Certificates) > 0 || config.GetCertificate != nil || config.GetConfigForClient != nil
  3485  	if !configHasCert || certFile != "" || keyFile != "" {
  3486  		var err error
  3487  		config.Certificates = make([]tls.Certificate, 1)
  3488  		config.Certificates[0], err = tls.LoadX509KeyPair(certFile, keyFile)
  3489  		if err != nil {
  3490  			return err
  3491  		}
  3492  	}
  3493  
  3494  	tlsListener := tls.NewListener(l, config)
  3495  	return s.Serve(tlsListener)
  3496  }
  3497  
  3498  func (s *Server) protocols() Protocols {
  3499  	if s.Protocols != nil {
  3500  		return *s.Protocols // user-configured set
  3501  	}
  3502  
  3503  	// The historic way of disabling HTTP/2 is to set TLSNextProto to
  3504  	// a non-nil map with no "h2" entry.
  3505  	_, hasH2 := s.TLSNextProto["h2"]
  3506  	http2Disabled := s.TLSNextProto != nil && !hasH2
  3507  
  3508  	// If GODEBUG=http2server=0, then HTTP/2 is disabled unless
  3509  	// the user has manually added an "h2" entry to TLSNextProto
  3510  	// (probably by using x/net/http2 directly).
  3511  	if http2server.Value() == "0" && !hasH2 {
  3512  		http2Disabled = true
  3513  	}
  3514  
  3515  	var p Protocols
  3516  	p.SetHTTP1(true) // default always includes HTTP/1
  3517  	if !http2Disabled {
  3518  		p.SetHTTP2(true)
  3519  	}
  3520  	return p
  3521  }
  3522  
  3523  // adjustNextProtos adds or removes "http/1.1" and "h2" entries from
  3524  // a tls.Config.NextProtos list, according to the set of protocols in protos.
  3525  func adjustNextProtos(nextProtos []string, protos Protocols) []string {
  3526  	// Make a copy of NextProtos since it might be shared with some other tls.Config.
  3527  	// (tls.Config.Clone doesn't do a deep copy.)
  3528  	//
  3529  	// We could avoid an allocation in the common case by checking to see if the slice
  3530  	// is already in order, but this is just one small allocation per connection.
  3531  	nextProtos = slices.Clone(nextProtos)
  3532  	var have Protocols
  3533  	nextProtos = slices.DeleteFunc(nextProtos, func(s string) bool {
  3534  		switch s {
  3535  		case "http/1.1":
  3536  			if !protos.HTTP1() {
  3537  				return true
  3538  			}
  3539  			have.SetHTTP1(true)
  3540  		case "h2":
  3541  			if !protos.HTTP2() {
  3542  				return true
  3543  			}
  3544  			have.SetHTTP2(true)
  3545  		}
  3546  		return false
  3547  	})
  3548  	if protos.HTTP2() && !have.HTTP2() {
  3549  		nextProtos = append(nextProtos, "h2")
  3550  	}
  3551  	if protos.HTTP1() && !have.HTTP1() {
  3552  		nextProtos = append(nextProtos, "http/1.1")
  3553  	}
  3554  	return nextProtos
  3555  }
  3556  
  3557  // trackListener adds or removes a net.Listener to the set of tracked
  3558  // listeners.
  3559  //
  3560  // We store a pointer to interface in the map set, in case the
  3561  // net.Listener is not comparable. This is safe because we only call
  3562  // trackListener via Serve and can track+defer untrack the same
  3563  // pointer to local variable there. We never need to compare a
  3564  // Listener from another caller.
  3565  //
  3566  // It reports whether the server is still up (not Shutdown or Closed).
  3567  func (s *Server) trackListener(ln *net.Listener, add bool) bool {
  3568  	s.mu.Lock()
  3569  	defer s.mu.Unlock()
  3570  	if s.listeners == nil {
  3571  		s.listeners = make(map[*net.Listener]struct{})
  3572  	}
  3573  	if add {
  3574  		if s.shuttingDown() {
  3575  			return false
  3576  		}
  3577  		s.listeners[ln] = struct{}{}
  3578  		s.listenerGroup.Add(1)
  3579  	} else {
  3580  		delete(s.listeners, ln)
  3581  		s.listenerGroup.Done()
  3582  	}
  3583  	return true
  3584  }
  3585  
  3586  func (s *Server) trackConn(c *conn, add bool) {
  3587  	s.mu.Lock()
  3588  	defer s.mu.Unlock()
  3589  	if s.activeConn == nil {
  3590  		s.activeConn = make(map[*conn]struct{})
  3591  	}
  3592  	if add {
  3593  		s.activeConn[c] = struct{}{}
  3594  	} else {
  3595  		delete(s.activeConn, c)
  3596  	}
  3597  }
  3598  
  3599  func (s *Server) idleTimeout() time.Duration {
  3600  	if s.IdleTimeout != 0 {
  3601  		return s.IdleTimeout
  3602  	}
  3603  	return s.ReadTimeout
  3604  }
  3605  
  3606  func (s *Server) readHeaderTimeout() time.Duration {
  3607  	if s.ReadHeaderTimeout != 0 {
  3608  		return s.ReadHeaderTimeout
  3609  	}
  3610  	return s.ReadTimeout
  3611  }
  3612  
  3613  func (s *Server) doKeepAlives() bool {
  3614  	return !s.disableKeepAlives.Load() && !s.shuttingDown()
  3615  }
  3616  
  3617  func (s *Server) shuttingDown() bool {
  3618  	return s.inShutdown.Load()
  3619  }
  3620  
  3621  // SetKeepAlivesEnabled controls whether HTTP keep-alives are enabled.
  3622  // By default, keep-alives are always enabled. Only very
  3623  // resource-constrained environments or servers in the process of
  3624  // shutting down should disable them.
  3625  func (s *Server) SetKeepAlivesEnabled(v bool) {
  3626  	if v {
  3627  		s.disableKeepAlives.Store(false)
  3628  		return
  3629  	}
  3630  	s.disableKeepAlives.Store(true)
  3631  
  3632  	// Close idle HTTP/1 conns:
  3633  	s.closeIdleConns()
  3634  
  3635  	// TODO: Issue 26303: close HTTP/2 conns as soon as they become idle.
  3636  }
  3637  
  3638  func (s *Server) logf(format string, args ...any) {
  3639  	if s.ErrorLog != nil {
  3640  		s.ErrorLog.Printf(format, args...)
  3641  	} else {
  3642  		log.Printf(format, args...)
  3643  	}
  3644  }
  3645  
  3646  // logf prints to the ErrorLog of the *Server associated with request r
  3647  // via ServerContextKey. If there's no associated server, or if ErrorLog
  3648  // is nil, logging is done via the log package's standard logger.
  3649  func logf(r *Request, format string, args ...any) {
  3650  	s, _ := r.Context().Value(ServerContextKey).(*Server)
  3651  	if s != nil && s.ErrorLog != nil {
  3652  		s.ErrorLog.Printf(format, args...)
  3653  	} else {
  3654  		log.Printf(format, args...)
  3655  	}
  3656  }
  3657  
  3658  // ListenAndServe listens on the TCP network address addr and then calls
  3659  // [Serve] with handler to handle requests on incoming connections.
  3660  // Accepted connections are configured to enable TCP keep-alives.
  3661  //
  3662  // The handler is typically nil, in which case [DefaultServeMux] is used.
  3663  //
  3664  // ListenAndServe always returns a non-nil error.
  3665  func ListenAndServe(addr string, handler Handler) error {
  3666  	server := &Server{Addr: addr, Handler: handler}
  3667  	return server.ListenAndServe()
  3668  }
  3669  
  3670  // ListenAndServeTLS acts identically to [ListenAndServe], except that it
  3671  // expects HTTPS connections. Additionally, files containing a certificate and
  3672  // matching private key for the server must be provided. If the certificate
  3673  // is signed by a certificate authority, the certFile should be the concatenation
  3674  // of the server's certificate, any intermediates, and the CA's certificate.
  3675  func ListenAndServeTLS(addr, certFile, keyFile string, handler Handler) error {
  3676  	server := &Server{Addr: addr, Handler: handler}
  3677  	return server.ListenAndServeTLS(certFile, keyFile)
  3678  }
  3679  
  3680  // ListenAndServeTLS listens on the TCP network address s.Addr and
  3681  // then calls [ServeTLS] to handle requests on incoming TLS connections.
  3682  // Accepted connections are configured to enable TCP keep-alives.
  3683  //
  3684  // Filenames containing a certificate and matching private key for the
  3685  // server must be provided if neither the [Server]'s TLSConfig.Certificates
  3686  // nor TLSConfig.GetCertificate are populated. If the certificate is
  3687  // signed by a certificate authority, the certFile should be the
  3688  // concatenation of the server's certificate, any intermediates, and
  3689  // the CA's certificate.
  3690  //
  3691  // If s.Addr is blank, ":https" is used.
  3692  //
  3693  // ListenAndServeTLS always returns a non-nil error. After [Server.Shutdown] or
  3694  // [Server.Close], the returned error is [ErrServerClosed].
  3695  func (s *Server) ListenAndServeTLS(certFile, keyFile string) error {
  3696  	if s.shuttingDown() {
  3697  		return ErrServerClosed
  3698  	}
  3699  	addr := s.Addr
  3700  	if addr == "" {
  3701  		addr = ":https"
  3702  	}
  3703  
  3704  	ln, err := net.Listen("tcp", addr)
  3705  	if err != nil {
  3706  		return err
  3707  	}
  3708  
  3709  	defer ln.Close()
  3710  
  3711  	return s.ServeTLS(ln, certFile, keyFile)
  3712  }
  3713  
  3714  // setupHTTP2_ServeTLS conditionally configures HTTP/2 on
  3715  // s and reports whether there was an error setting it up. If it is
  3716  // not configured for policy reasons, nil is returned.
  3717  func (s *Server) setupHTTP2_ServeTLS() error {
  3718  	s.nextProtoOnce.Do(s.onceSetNextProtoDefaults)
  3719  	return s.nextProtoErr
  3720  }
  3721  
  3722  // setupHTTP2_Serve is called from (*Server).Serve and conditionally
  3723  // configures HTTP/2 on s using a more conservative policy than
  3724  // setupHTTP2_ServeTLS because Serve is called after tls.Listen,
  3725  // and may be called concurrently. See shouldConfigureHTTP2ForServe.
  3726  //
  3727  // The tests named TestTransportAutomaticHTTP2* and
  3728  // TestConcurrentServerServe in server_test.go demonstrate some
  3729  // of the supported use cases and motivations.
  3730  func (s *Server) setupHTTP2_Serve() error {
  3731  	s.nextProtoOnce.Do(s.onceSetNextProtoDefaults_Serve)
  3732  	return s.nextProtoErr
  3733  }
  3734  
  3735  func (s *Server) onceSetNextProtoDefaults_Serve() {
  3736  	if s.shouldConfigureHTTP2ForServe() {
  3737  		s.onceSetNextProtoDefaults()
  3738  	}
  3739  }
  3740  
  3741  var http2server = godebug.New("http2server")
  3742  
  3743  // onceSetNextProtoDefaults configures HTTP/2, if the user hasn't
  3744  // configured otherwise. (by setting s.TLSNextProto non-nil)
  3745  // It must only be called via s.nextProtoOnce (use s.setupHTTP2_*).
  3746  func (s *Server) onceSetNextProtoDefaults() {
  3747  	if omitBundledHTTP2 {
  3748  		return
  3749  	}
  3750  	p := s.protocols()
  3751  	if !p.HTTP2() && !p.UnencryptedHTTP2() {
  3752  		return
  3753  	}
  3754  	if http2server.Value() == "0" {
  3755  		http2server.IncNonDefault()
  3756  		return
  3757  	}
  3758  	if _, ok := s.TLSNextProto["h2"]; ok {
  3759  		// TLSNextProto already contains an HTTP/2 implementation.
  3760  		// The user probably called golang.org/x/net/http2.ConfigureServer
  3761  		// to add it.
  3762  		return
  3763  	}
  3764  	conf := &http2Server{}
  3765  	s.nextProtoErr = http2ConfigureServer(s, conf)
  3766  }
  3767  
  3768  // TimeoutHandler returns a [Handler] that runs h with the given time limit.
  3769  //
  3770  // The new Handler calls h.ServeHTTP to handle each request, but if a
  3771  // call runs for longer than its time limit, the handler responds with
  3772  // a 503 Service Unavailable error and the given message in its body.
  3773  // (If msg is empty, a suitable default message will be sent.)
  3774  // After such a timeout, writes by h to its [ResponseWriter] will return
  3775  // [ErrHandlerTimeout].
  3776  //
  3777  // TimeoutHandler supports the [Pusher] interface but does not support
  3778  // the [Hijacker] or [Flusher] interfaces.
  3779  func TimeoutHandler(h Handler, dt time.Duration, msg string) Handler {
  3780  	return &timeoutHandler{
  3781  		handler: h,
  3782  		body:    msg,
  3783  		dt:      dt,
  3784  	}
  3785  }
  3786  
  3787  // ErrHandlerTimeout is returned on [ResponseWriter] Write calls
  3788  // in handlers which have timed out.
  3789  var ErrHandlerTimeout = errors.New("http: Handler timeout")
  3790  
  3791  type timeoutHandler struct {
  3792  	handler Handler
  3793  	body    string
  3794  	dt      time.Duration
  3795  
  3796  	// When set, no context will be created and this context will
  3797  	// be used instead.
  3798  	testContext context.Context
  3799  }
  3800  
  3801  func (h *timeoutHandler) errorBody() string {
  3802  	if h.body != "" {
  3803  		return h.body
  3804  	}
  3805  	return "<html><head><title>Timeout</title></head><body><h1>Timeout</h1></body></html>"
  3806  }
  3807  
  3808  func (h *timeoutHandler) ServeHTTP(w ResponseWriter, r *Request) {
  3809  	ctx := h.testContext
  3810  	if ctx == nil {
  3811  		var cancelCtx context.CancelFunc
  3812  		ctx, cancelCtx = context.WithTimeout(r.Context(), h.dt)
  3813  		defer cancelCtx()
  3814  	}
  3815  	r = r.WithContext(ctx)
  3816  	done := make(chan struct{})
  3817  	tw := &timeoutWriter{
  3818  		w:   w,
  3819  		h:   make(Header),
  3820  		req: r,
  3821  	}
  3822  	panicChan := make(chan any, 1)
  3823  	go func() {
  3824  		defer func() {
  3825  			if p := recover(); p != nil {
  3826  				panicChan <- p
  3827  			}
  3828  		}()
  3829  		h.handler.ServeHTTP(tw, r)
  3830  		close(done)
  3831  	}()
  3832  	select {
  3833  	case p := <-panicChan:
  3834  		panic(p)
  3835  	case <-done:
  3836  		tw.mu.Lock()
  3837  		defer tw.mu.Unlock()
  3838  		dst := w.Header()
  3839  		maps.Copy(dst, tw.h)
  3840  		if !tw.wroteHeader {
  3841  			tw.code = StatusOK
  3842  		}
  3843  		w.WriteHeader(tw.code)
  3844  		w.Write(tw.wbuf.Bytes())
  3845  	case <-ctx.Done():
  3846  		tw.mu.Lock()
  3847  		defer tw.mu.Unlock()
  3848  		switch err := ctx.Err(); err {
  3849  		case context.DeadlineExceeded:
  3850  			w.WriteHeader(StatusServiceUnavailable)
  3851  			io.WriteString(w, h.errorBody())
  3852  			tw.err = ErrHandlerTimeout
  3853  		default:
  3854  			w.WriteHeader(StatusServiceUnavailable)
  3855  			tw.err = err
  3856  		}
  3857  	}
  3858  }
  3859  
  3860  type timeoutWriter struct {
  3861  	w    ResponseWriter
  3862  	h    Header
  3863  	wbuf bytes.Buffer
  3864  	req  *Request
  3865  
  3866  	mu          sync.Mutex
  3867  	err         error
  3868  	wroteHeader bool
  3869  	code        int
  3870  }
  3871  
  3872  var _ Pusher = (*timeoutWriter)(nil)
  3873  
  3874  // Push implements the [Pusher] interface.
  3875  func (tw *timeoutWriter) Push(target string, opts *PushOptions) error {
  3876  	if pusher, ok := tw.w.(Pusher); ok {
  3877  		return pusher.Push(target, opts)
  3878  	}
  3879  	return ErrNotSupported
  3880  }
  3881  
  3882  func (tw *timeoutWriter) Header() Header { return tw.h }
  3883  
  3884  func (tw *timeoutWriter) Write(p []byte) (int, error) {
  3885  	tw.mu.Lock()
  3886  	defer tw.mu.Unlock()
  3887  	if tw.err != nil {
  3888  		return 0, tw.err
  3889  	}
  3890  	if !tw.wroteHeader {
  3891  		tw.writeHeaderLocked(StatusOK)
  3892  	}
  3893  	return tw.wbuf.Write(p)
  3894  }
  3895  
  3896  func (tw *timeoutWriter) writeHeaderLocked(code int) {
  3897  	checkWriteHeaderCode(code)
  3898  
  3899  	switch {
  3900  	case tw.err != nil:
  3901  		return
  3902  	case tw.wroteHeader:
  3903  		if tw.req != nil {
  3904  			caller := relevantCaller()
  3905  			logf(tw.req, "http: superfluous response.WriteHeader call from %s (%s:%d)", caller.Function, path.Base(caller.File), caller.Line)
  3906  		}
  3907  	default:
  3908  		tw.wroteHeader = true
  3909  		tw.code = code
  3910  	}
  3911  }
  3912  
  3913  func (tw *timeoutWriter) WriteHeader(code int) {
  3914  	tw.mu.Lock()
  3915  	defer tw.mu.Unlock()
  3916  	tw.writeHeaderLocked(code)
  3917  }
  3918  
  3919  // onceCloseListener wraps a net.Listener, protecting it from
  3920  // multiple Close calls.
  3921  type onceCloseListener struct {
  3922  	net.Listener
  3923  	once     sync.Once
  3924  	closeErr error
  3925  }
  3926  
  3927  func (oc *onceCloseListener) Close() error {
  3928  	oc.once.Do(oc.close)
  3929  	return oc.closeErr
  3930  }
  3931  
  3932  func (oc *onceCloseListener) close() { oc.closeErr = oc.Listener.Close() }
  3933  
  3934  // globalOptionsHandler responds to "OPTIONS *" requests.
  3935  type globalOptionsHandler struct{}
  3936  
  3937  func (globalOptionsHandler) ServeHTTP(w ResponseWriter, r *Request) {
  3938  	w.Header().Set("Content-Length", "0")
  3939  	if r.ContentLength != 0 {
  3940  		// Read up to 4KB of OPTIONS body (as mentioned in the
  3941  		// spec as being reserved for future use), but anything
  3942  		// over that is considered a waste of server resources
  3943  		// (or an attack) and we abort and close the connection,
  3944  		// courtesy of MaxBytesReader's EOF behavior.
  3945  		mb := MaxBytesReader(w, r.Body, 4<<10)
  3946  		io.Copy(io.Discard, mb)
  3947  	}
  3948  }
  3949  
  3950  // initALPNRequest is an HTTP handler that initializes certain
  3951  // uninitialized fields in its *Request. Such partially-initialized
  3952  // Requests come from ALPN protocol handlers.
  3953  type initALPNRequest struct {
  3954  	ctx context.Context
  3955  	c   *tls.Conn
  3956  	h   serverHandler
  3957  }
  3958  
  3959  // BaseContext is an exported but unadvertised [http.Handler] method
  3960  // recognized by x/net/http2 to pass down a context; the TLSNextProto
  3961  // API predates context support so we shoehorn through the only
  3962  // interface we have available.
  3963  func (h initALPNRequest) BaseContext() context.Context { return h.ctx }
  3964  
  3965  func (h initALPNRequest) ServeHTTP(rw ResponseWriter, req *Request) {
  3966  	if req.TLS == nil {
  3967  		req.TLS = &tls.ConnectionState{}
  3968  		*req.TLS = h.c.ConnectionState()
  3969  	}
  3970  	if req.Body == nil {
  3971  		req.Body = NoBody
  3972  	}
  3973  	if req.RemoteAddr == "" {
  3974  		req.RemoteAddr = h.c.RemoteAddr().String()
  3975  	}
  3976  	h.h.ServeHTTP(rw, req)
  3977  }
  3978  
  3979  // loggingConn is used for debugging.
  3980  type loggingConn struct {
  3981  	name string
  3982  	net.Conn
  3983  }
  3984  
  3985  var (
  3986  	uniqNameMu   sync.Mutex
  3987  	uniqNameNext = make(map[string]int)
  3988  )
  3989  
  3990  func newLoggingConn(baseName string, c net.Conn) net.Conn {
  3991  	uniqNameMu.Lock()
  3992  	defer uniqNameMu.Unlock()
  3993  	uniqNameNext[baseName]++
  3994  	return &loggingConn{
  3995  		name: fmt.Sprintf("%s-%d", baseName, uniqNameNext[baseName]),
  3996  		Conn: c,
  3997  	}
  3998  }
  3999  
  4000  func (c *loggingConn) Write(p []byte) (n int, err error) {
  4001  	log.Printf("%s.Write(%d) = ....", c.name, len(p))
  4002  	n, err = c.Conn.Write(p)
  4003  	log.Printf("%s.Write(%d) = %d, %v", c.name, len(p), n, err)
  4004  	return
  4005  }
  4006  
  4007  func (c *loggingConn) Read(p []byte) (n int, err error) {
  4008  	log.Printf("%s.Read(%d) = ....", c.name, len(p))
  4009  	n, err = c.Conn.Read(p)
  4010  	log.Printf("%s.Read(%d) = %d, %v", c.name, len(p), n, err)
  4011  	return
  4012  }
  4013  
  4014  func (c *loggingConn) Close() (err error) {
  4015  	log.Printf("%s.Close() = ...", c.name)
  4016  	err = c.Conn.Close()
  4017  	log.Printf("%s.Close() = %v", c.name, err)
  4018  	return
  4019  }
  4020  
  4021  // checkConnErrorWriter writes to c.rwc and records any write errors to c.werr.
  4022  // It only contains one field (and a pointer field at that), so it
  4023  // fits in an interface value without an extra allocation.
  4024  type checkConnErrorWriter struct {
  4025  	c *conn
  4026  }
  4027  
  4028  func (w checkConnErrorWriter) Write(p []byte) (n int, err error) {
  4029  	n, err = w.c.rwc.Write(p)
  4030  	if err != nil && w.c.werr == nil {
  4031  		w.c.werr = err
  4032  		w.c.cancelCtx()
  4033  	}
  4034  	return
  4035  }
  4036  
  4037  func numLeadingCRorLF(v []byte) (n int) {
  4038  	for _, b := range v {
  4039  		if b == '\r' || b == '\n' {
  4040  			n++
  4041  			continue
  4042  		}
  4043  		break
  4044  	}
  4045  	return
  4046  }
  4047  
  4048  // tlsRecordHeaderLooksLikeHTTP reports whether a TLS record header
  4049  // looks like it might've been a misdirected plaintext HTTP request.
  4050  func tlsRecordHeaderLooksLikeHTTP(hdr [5]byte) bool {
  4051  	switch string(hdr[:]) {
  4052  	case "GET /", "HEAD ", "POST ", "PUT /", "OPTIO":
  4053  		return true
  4054  	}
  4055  	return false
  4056  }
  4057  
  4058  // MaxBytesHandler returns a [Handler] that runs h with its [ResponseWriter] and [Request.Body] wrapped by a MaxBytesReader.
  4059  func MaxBytesHandler(h Handler, n int64) Handler {
  4060  	return HandlerFunc(func(w ResponseWriter, r *Request) {
  4061  		r2 := *r
  4062  		r2.Body = MaxBytesReader(w, r.Body, n)
  4063  		h.ServeHTTP(w, &r2)
  4064  	})
  4065  }
  4066  

View as plain text